Hi
follow up, just in case anyone else looks
did several restarts and power off of the server, not just domino, but the problem persisted
had a look with netstat and could see connections being established on 50125 and 50126, waited a while hoping to see a failure or timeout event, but none happened in the time I was watching, which is kind of consistent because it wasn't happening for all device sync requests, only some of them and infrequently
given your comments I looked at the windows system
the day prior to installing 901 FP9 I had separately installed two windows updates, one was a monthly security rollup kb4034681, the other was a .net optional update kb3186539
uninstalled the .net update and restarted - running 2hrs so far and the timeout problem timeout has not reappeared
The few devices that had the problem have sync'd several times and seem to be back to working without any issues
if it recurs I'll look at the PMR option
thanks
Keith