Heartbeat loss is typically a network related issue, where congestion or bottlenecks can prevent
remote APs from keeping timely synchronization with the vSZ controller(s). Can you measure the
round-trip time (RTT) from the APs that are having trouble re-connecting? The AP cert refresh is
important, and enabling lwapp2scg to recognize ZD APs, if not firmware converted to base Solo
code. To try converting an AP, use 220.127.116.11.1347 from this link:https://support.ruckuswireless.com/software/1017-zoneflex-solo-access-point-104-0-0-0-1347-ga-softwa...
When factory defaulted, you'll need DHCP option 43, or DNS to point your AP to the vSZ. (or AP
CLI command 'set scg ip a.b.c.d' and 'reboot').
Please let us know, and there's no reason TS should have told you to stay off SZ 3.5.1 btw.