So, I moved 100+ APs, 3502s, using Prime to a WLC that had updated firmware. The 3502s are not compatible with 18.104.22.168, so the WLC I moved it to showed some CAPWAP errors stating, " no license present with the AP trying to join". We disabled Licensing on it. Using: Config ap cert-expiry-ingore mic enable/disable. It took about 10-15 mins and the APs joined a WLC that was compatible with the 3502s. I then used prime to reconfigure them to the appropriate WLC.
You always need to look at the compatibility matrix. Never assume when you upgrade or downgrade or introduce a new device. If you consoled into the ap, you would see a message stating an error about the code not being supported. Anyway's, if you don't have it, here is the link to the matrix:
"config ap cert-expiry-ingore mic enable/disable" has nothing to do with licensing - it disables/enables certificate date validity checks.
Like @Scott Fella said you need to read release notes, deployment guides, TAC recommendations and support matrix docs before embarking on major changes.
In this case if "config ap cert-expiry-ingore mic enable/disable" solved your problem then you were hitting the certificate expiry issue very comprehensively documented (and referenced dozens of times on these forums) in the field notice: