Upgraded from latest bugfix.
7.5 stable.
then rebooted for routerboard upgrade.
cpu 100%
100% is wireless, according to profiler.

error appeared in the logs:

error while running customized default configuration script: std failure: timeout (13)

then after 1-2 min, cpu normal, router is working correctly.

check system resources RAM Free Memory

hAP Lite only has 32MB, latest releases use more RAM so consider Downgrade to previous version where you achieve stable performance

Hello. I know.
The ram usage is similar to ros 6.
After the heavy cpu on boot, the router is working normally with no issues.

Interesting the router upgraded to the ros 7 flawlessy when the hap ac v1 and v2 wasnt able to do that because of disk space issue.