[GPS_Standard] Parameter corruption - cause?

[Mike W]

good morn folks, I'm experiencing intermittant and random parameter corruption 
on both of my VE2ZAZ boards, they are running 24/7and don't corrupt at the 
same time. Driven from different 1pps sources and different psu's, they are 
both running the latest software. This has only started after upgrading the 
software. Niether have shown this behaviour on the initial version of the 
software.
Any ideas appreciated, thans, Mike G8NXD