FreePBX 17 and Digium A-series phones

I have a bunch of the older Digium A-series “Asterisk” phones (mostly A-20’s with a single A-25) which I’ve been using successfully for several years now with FreePBX 16.

After I upgraded to FreePBX 17 (restoring my FreePBX 16 configuration from a backup), calls randomly stopped reaching the phones. They’re registered and can place outgoing calls at any time. If an incoming call comes in without about 20 seconds of the end of an outgoing call the phone will ring. Otherwise, phone shows no sign of seeing the incoming call and it goes straight to voicemail.

At the moment, I’ve reverted back to FreePBX 16 because that version WORKS.

Any suggestions on what might be the problem here?