3DR radios no longer connect after upgrade to AC3.1 & Sik1.8

A weird thing, after running ACv3.1rc7 for quite a while and the 1.7 Sik firmware on the 3DR 433 radio’s, I upgraded both, the radios first to v1.8.1 (and if I recall correctly they worked fine) and then the quad to AC3.1 final.

Now they either won’t connect, or connect very slowly and incompletely. Nothing else has changed

Any ideas?

I can’t seem to find the 1.7 hex file to roll back the firmware on the radios.

After two hours of fiddling I found the radios work with v3.1rc8 but not with v3.1 final

How can that be?