At first, I thought it was a bug or an issue. I was going to try to contact Engrave, but then I found that you can simply not replace the posting key if you want to keep social activities in the account.
Check this tutorial for more info:
https://peakd.com/engrave/@engrave/how-to-use-hive-ledger-wallet
This is one of the important steps. If you activate this, you must remove the account and add it again if you want to use your posting key.
And the rewards would not be forever lost, it just means they can't be claimed. So they will appear as pending balances like this:
Do I need to unlink my account from Leiger and use the original keys to remove the rewards?
To claim them, yes. Then you can add the account again.