I recently set up a 24-ch preamp rack with 3 Presonus Digimax units. An older 48k model I had on hand and the two 96k units are recent used purchases. I had tested out the rack with a laptop/RME Digiface successfully a month or so ago and it ran just as I have grown accustomed to with a different rack setup. I use word clock for sync/lock and use the ADAT outs for my audio inputs.

Today, one of the Presonus 96k units has started losing its ability to maintain sync when it's set to external clock - which is how I've always used these. This happens whether it is run by itself, or part of the chain of 3 units and it appears to not make a difference of what position it is in in the chain.

It will work as the master clock, however, with the RME set to Autosync.
It also works when I first start it up and I just noticed that it loses it sync sometime after it's been on awhile, leading me to suspect a heat-related issue..... but I have no idea where to look to find the problem or a solution.

Does anybody have any suggestions that might help me trace the issue and maybe find a solution to get it to work in external clock mode again? Presonus has stopped servicing these units quite a few years ago, but they still work plenty fine for my live recording needs, but I don't know anyone to take it to for service, if the problem goes beyond my ever dwindling tech abilities.