How can a seed generate the wrong addresses? What happened:
I created a wallet with my backup seed.
Then I sent to the generated wallet addresses:

BTC: bc1q70shswq68tx5p2e2mms34up5jpxeqfyzp3let6

Everything was ok and I had access to my funds in the Coinbase Wallet App.
Then I wanted to send BTC back to Coinbase to trade it.
But I got the same error as the guy on twitter: https://twitter.com/scottyboi78/status/1357378323270291457/photo/1
Calculating the fees was actually not the problem.
Then I restored the wallet with my recovery seed multiple times on my iPhone. I also tried Android Emulator with Android Studio and the official Coinbase Wallet App.
The result is always the same:

BTC: bc1qgdw5aqhd8uz7rl4cxkkk66u33swsnmzl6aeaqg (something wrong)

How can it happen that the SAME seed results in DIFFERENT addresses for BTC!
That should not be possible!
Please help me I lost all my money and it is there in the Blockchain but I can't access it because the seed generation has a bug (I think at least)!
Once you use a BTC receiving address once, any good wallet will not display the same address again; they'll display the next address in the chain (since your seed derives to a large chain of different addresses). The coins are not lost, your wallet balance should still be there, and the wallet will still track the old address, it just won't display the old addresses by default to discourage reuse of the old address.