Thanks for your input.
I think this is a different issue that the one I was trying to figure out though. The initial edited file when saved in PS would always appear straight away back in LR, it was any subsequent edit in PS, after the file was closed then reopened, that was not getting updated in LR unless I did a close/open of LR, or waited a while, or tried to force a synch. I also had some odd thumbnail appearances (sometime seeming to update, sometimes not).
For my system, as I posted in the last entry or 2, it was fully resolved after testing with files stored on internal Raid 0 SATA SSDs, while the initial testing that was giving me problems was on files on a spinning HD in an external TB3 enclosure. All the testing was done when PS was empty (ie it had no files open except the one moving there from LR).
My system has 64GB RAM. LR cache and catalog are on a separate M2 drive than the OS which is also on an M2 drive.