Instant On - Wireless

Version 2.9.0 has made many things worse.
Setup
2 x AP 22
1 x AP 15
1930 8 Port
1930 8 Port Poe

Especially on the AP 15, I can only get a very slow connection speeds with iPhones. In general, no AP works reliably any more
Is it possible to downgrade to version 2.8.0 again?

After a restart of the access points it seems to be back to normal.

However, I still have the question if downgrades are theoretically possible.

Software downgrades are not possible with the cloud management.