I'm experiencing a similar problem to other AGL customers in the posts. Since 7th of July 2021, my AGL app has not shown solar feed in to grid or actual usage, only estimates of usage. I have uninstalled and downloaded the AGL app a few times but this has not resolved the issue. (see screenshot attached).
Panels degrade overtime, but you'll system will still be providing more than enough. I got mine start of last year and my bill completely disappeared, I'm happy I bought it. Down in Vic our feed in is only 10.2c, but I did find out recently that I can negotiate with my provider and that'll be for another day, some competitors down here do a 15.2 feed in tarrif.