Strava/TR power recording significantly lower than Garmin

Hi all, I’m hoping for some insight here. I’ve looked into this issue a little bit but the topics that I find seem to all be referencing Strava showing a higher power than Garmin, where I’m having the opposite issue.

Specifically, I’ve noticed in my races this summer that Strava is showing an average power about 20-40 watts lower than what Garmin is showing. My race this weekend was even a bigger difference, with Garmin showing 250W, and Strava (and TR) showing 186! Which is why I now want to look into the issue.

To start with, I’m guessing this could just be a problem with my power meter because I’ve only seen this discrepancy in races and I’ve got a different set up on my race bike than my training bike, and the power meter on my race bike is fairly old (about 8 years) so not sure if that should be an issue. The firmware is up to date according to the Stages app. Garmin Edge 510 is set to include zeroes.

I wanted to reach out to see if anyone has experienced anything like this or has any ideas/thoughts. Any help would be much appreciated!

Edit: Now I’m thinking this might 100% be a Garmin problem. Yesterday Garmin Connect had my 20 min max avg at 260, now it’s saying 189, but still showing a 250 watt average for the entire 40 min. race…