Had a couple of problems a few years ago that I chased for a couple months at least. Timing would move on its own particularly when the engine would heat sink.
Set everything up at the track in my pit running good drove perfect to the lanes. Sat with hood closed for half hour start the car to make a run black smoke could not do a burnout barely ran driving it off the track. About half way to my pit it starts running fine. WTF?
Fooled with it a bit then just packed up and went home that evening. Decided until I figured it out the car is parked.
There were 2 problems:
Am using the MSD dual synch distributor my engine is a tune port Chevy and wanted to run sequential. The pickup under the cap which is the crank signal was not tightened correctly at the factory even with the silicon they apply when the engine would get hot the pickup would move changing the timing. Tech West Racing gave me the heads up on that issue MSD tested the distributor of course there was not problem replaced the part with a little conversation..............
The second issue had me throwing stuff.
Would lock the timing at idle in the ECU then manually set timing with timing light. Verified the laptop and with timing light on the damper matched engine running good. Shut the car down unlocked timing, start it and runs like crap: timing moved 30 degrees.
Was completely lost it was hot as hell frustrating and near a meltdown. Took a break and decided to check every menu, every table and switch. XFI has a switch for Flex Fuel and a timing change table it operates if you use it and have the sensor. Was aware of it but wrongly assumed if the switch to enable the feature was OFF the table had no influence. Ahemm............
For ****s and giggles since had sweat out my 5th or 6th bottle of water checked the table and saw it was set to change timing 30 degrees. Zeroed it across the table made sure it was downloaded to the ECU shut down and restated the ECU checked to verify then started the car finally running good timing matched. Later found out FAST had a PDF and Video outlining what to look at and changes to make when using the software version had updated the ECU with. I was throwing stuff for a while afterword.
Keep in mind I don't normally throw stuff my nature as an Italian is to blow everything to smithereens so normally control that just calm down and move on since getting locked up or blown up is not an option.
Check all tables and switches you are using and not using.
Software is not as good as we think. If your not using a feature make sure it is switched off and the table is not in play.
If you are using a long USB cable to reach the car from inside the trailer they do not last forever there is electronics which boost the data over the long length it breaks down and fails. Chased that for weeks in 2018.