Master Seed from Mycellium does not concord with address Mycellium app generated for me Created MYCELLIUM wallet in 2017 - copied down Master Seed, been transacting ever since.
Upgrades of various phones, always reinstalled latest Mycellium and used master-seed to restore, no issues.
Last week, app was &quot;acting up&quot; -- didn't want to sync and seemed to hang.  I decided to delete it and reinstall/restore from master-seed.  This time, incorrect balance is shown, and transaction log as well as looking on blockchain of public key shows no more transactions after 2018 ?!  (even though been busy until last week!)
Used this site https://iancoleman.io/bip39/ to generate the derived addresses from my master seed.  Seems to be accurate as the first 10 addresses are indeed mine and show me what MyCellium shows me.  However, when I do a search (in the pool of derived addresses) for a Mycellium generated receiving address I successfully used last week ... that address is NOT found ?!   I assume the addresses are used sequentially?  I generated 5000 addresses and still can't find that address in there!
Any insight/help/etc would be greatly appreciated!  I've never imported other private keys into MyCellium, only used the addresses provided by the app, and created another HD wallet from within the app.
Any chance to recover my lost coins ?
Used this site https://iancoleman.io/bip39/ to generate the derived addresses from my master seed

Please do not enter seed on any website. It's only safe if you run it locally on your machine from https://github.com/iancoleman/bip39

Any chance to recover my lost coins ?

I would suggest restoring wallet in Electrum. You can follow the steps mentioned in this answer: https://bitcoin.stackexchange.com/a/99441/
Basic things to keep in mind: Either system used for wallet is offline or not affected with malwares, download from original source, verify it and never share your seed with anyone else.
Also for gap limit refer to: https://electrum.readthedocs.io/en/latest/faq.html#gap-limit and https://bitcoin.stackexchange.com/a/98919/