4 BTC sent to a random address?

I just managed to get access to my dad’s old Blockchain.com wallet from 2016. When I tried to transfer 1 BTC to Coinbase, it ended up sending 5 instead. Checking the transaction id, I saw that 1 BTC went to Coinbase like it was supposed to, but the extra 4 BTC went to some random address. What the heck happened? How can I get those 4 BTC back? I’ve tried contacting Blockchain.com support, but no response yet.

Probably the 4 BTC is sent to a change address which is part of your bitcoin address. You have nothing to be worried about. If you check your wallet, you will see the remaining 4 BTC on your wallet. If it happens that you did not see your coins, import your seed phrase on Bluewallet wallet or Electrum. If you see your coins there, better to create a new wallet on the Bluewallet or Electrum and send the remaining coins there because blockchain.com wallet is close source.

Thank you!  I read about change address, and am hoping that is the case, but I do not see my coins on the blockchain.com wallet.  So to recover these funds, I should download electrum wallet and import my seed phrase?  Is this safe? Thank you so much.

Yes, Electrum is safe. Electrum official site: https://electrum.org/ Alternative. Bluewallet: https://bluewallet.io/ You can use this guide but do not add passphrase if the wallet does not have it:

Personally, I'd stay away from Blockchain. In my experience, they aren't the most trustworthy, and they've had issues with some pretty significant bugs in the past. Once you resolve your current problem, move your bitcoins to an open source wallet (preferably move most of it to cold storage).

So I used my seed to open my wallet using bluewallet on mobile, and I do not see those 4 bitcoin in this wallet either, it is the same balance as the blockchain.com wallet, still missing 4 BTC! If this helps it says "Imported HD Legacy (BIP44 P@PKH)" for the wallet that i imported.. but it is the same balance as the blockchain.com wallet.  How do I get to this supposed "change address" that has my 4 BTC? Would it be helpful / safe to share the transaction id here?

That will slightly help others to identify the address where the change is sent and "guess" where it belongs to. It's safe but not good for your privacy if you don't want anyone to know your address(es). Try to follow this sticky post on what other information to include to your next reply: Tech Support Help Request Format

Electrum isn't safe if your computer isn't safe. With 5 Bitcoin, OP should get a decent hardware wallet (like Trezor, not Ledger) to keep his coins safe. You should STOP messing around on hot wallets on different devices! Each new wallet you enter the seed phrase on increases the chance of losing your Bitcoins. Figure out what to do first, figure out if it's a change address, learn how to use cold wallets on offline systems, and only then continue. Chances are you didn't lose those 4 Bitcoins yet. Don't mess up now! @OP: you should ignore any PMs you may receive. Scammers are preying on Newbies.

I heard back from blockchain support, they are instructing me to send a dust transaction from the blockchain wallet to a specific address.  They say this address belongs to me and sending this dust transaction will trigger an update to the wallet, rectifying the issue.  Because I used the seed to open a blue wallet, will this now throw everything off?  I am also concerned with sending another transaction, although small, to another address, how do I know the blockchain wallet won't again send a large amount of bitcoin to another wallet?  Should i send the majority of my remaining BTC on blockchain.com to coinbase first before attempting this dust transaction? This is extremely stressful..

Sending dust amount doesn't change anything and look like a red flag? Are you sure the response is from the official support? If you have the seeds and already imported it into blue wallet, you must find the balance in it and if it's not there then it must be stolen probably via clipboard malware. Don't send dust amount, just try to look the 4btc is sent back to the change address or it belongs to different wallet.

They are saying that sending this dust transaction will resolve the problem caused by the "gap limit" (they are saying there has been a gap on the receiving address that I have), which may have affected my ability to see my funds. Once the transaction is confirmed, it will trigger an update in my wallet, rectifying the issue. This is the official Blockchain support, and I reached out to two separate reps from two separate emails and received the same instructions.

If this is truly a gap limit issue, on Bluewallet, you could try the following and see if the missing address shows up: My Wallet -> ... -> Show Addresses -> [Receive] or [Change]   screenshot: https://i.imgur.com/s2FIuaa.png

I've also confirmed via xpub that the funds are in an address listed under my xpub!  This is good news right?

Yes that's good news!

Forget about blockchain, get an offline Live Linux system, get IanColeman's site (save it to an USB stick to get it on your offline system), and search until you find the private key to your address. If you found it through xpub, you know how far to search.

Fully support this. Each time that you go to Blockchain to try go get help or search for other options, you may eventually be led to a scam website that will trick you into providing access to your wallet. The wisest decision for you at the moment would be to retrieve all of your bitcoin into an environment solely controlled by you and not a 3rd party.

If you recovered it successfully, you have access to it so that you can get its private key too. You can import it to Electrum wallet, choose BIP39, and I also recommend you to move all your bitcoin in blockchain.com wallet to a new wallet created by Electrum (offline). Blockchain.com wallet is a close source wallet, it's not recommended. Electrum wallet is open source wallet, it's better for Bitcoin users. Verify the Electrum wallet too. [GUIDE] How to Safely Download and Verify Electrum. The 4 BTC likely sent to your address, that is a change address too. However the change address belongs to your same wallet, that means you should see 4 BTC in your wallet balance. Please confirm, did you see it in your wallet balance? You see it in balance, means you didn't lose your bitcoin. What is the "Change" address on bitcoin wallet ? read to know !

I share LoyceV's advise for OP to get a decent hardware wallet to secure his inherited funds. It's already quite risky to setup a hot wallet on a mobile phone for such an amount as a few Bitcoin. On a mobile phone that's used for all sorts of internet shit, that's insane, to be honest. OP clearly shows that he doesn't have basic knowledge how Bitcoin works, so the likelyhood that he messes up something is quite high. Keep your recovery words safe and offline. Do not ever input them on an online website. Learn the basics: https://learnmeabitcoin.com Learn how to use a hardware wallet correctly and stay away from the Ledger crap, there are decent open-source firmware alternatives out there.

Hardware wallets have many types, close-source, open-source, and crap like Ledger wallet with their terrible product, Ledger Recover service. [LIST] Open Source Hardware Wallets [GUIDE] How to buy a Hardware Wallet the right way Ledger Recover: What The Hell is Happening? List of Hardware wallet hacks.