This might not be easy, but any ideas how to take out a load of ridiculous spikes and drops to get, at least a semblance of a reflective TSS from my ride today. 790 TSS for 100 miles, Nah!!

Another punchy Max Power, Alan?! I had a couple of spikes that I got rid of post ride and everything is okay now. But this was from the immediate upload from the 530

Interestingly, I noticed in my training zones that my FTP was set at 790. Additionally, the Automatic FTP was turned on, again, with a ridiculous reading in that. So, whilst riding, I turned that off, and reset my power zones based on my actual real FTP . I know this won't cause the spikes, but it cause the challenging readings thereafter?
Ps this is on the new firmware and new GPS firmware
What generation of V3 battery doors do you have?
I'm seeing a number of resets.
The latest battery door version is Mark III. These have gold plated contact tips. If you don't have these contact Garmin Support and they will get you the Mark III doors along with some modified PCBs.
In the mean time could you check the contacts to make sure they are clean.