Access Point AP55C won't register with Central

Hi, we migrated a site from XG210 to XGS2300 withSFOS is 20.0.2. They have three Access Point APX320 and four Access Points AP55C. The APX320 work fine, but of course the AP55C don't work anymore with the XGS. Now we wanted to register the AP55C with Central but they always time out. We deactivated Wireless Protection on the local XGS and restarted the AP55C and we deleted them from the XGS. No luck.

Is there any way we can get this working still? We have another site where the AP55C still work fine with an XGS2100 via Central, but i think the SFOS is still on 19.x.x