When upgrading C25 identifi to 10.21.03.0010-1 : a lot of disconnection problems appeared with apple devices (iPad and iPhone : impossible to have a stable connection)
S7 from Samsung have no stable connection, but ip DHCP is ok (not possible with apple ios)
After some days, I have downgrade to 10.21.02.0017-1 and everything is ok
I think the AP reboot solves your problem NOT the downgrade!
Update your AP again to 10.21.03 and reboot the AP check if Problem occurs again.
I cannot imagine that 10.21.02 is more stable / have less issues as 10.21.03.
If you like you can up- or downgrade via "controlled" updates only one or two test APs to a new version not the whole EWC or all APs. Try it !