Help with Max HR please?

Hi All! Please be kind as it’s my first post here. A couple months ago I upgraded from a Lily Active 2 to a Venu 4. I’m an active 42F and focus primarily on weight training and HIIT type workouts.

I decided to try a suggested interval run, and afterward Garmin auto updated my max HR to 186. I’m actually not sure what it was before. The issue is that it is really impacting my workout and primary benefits, training readiness, calorie burn etc. I’m doing 75 Hard at the moment and my watch is telling me I’m maintaining and not working out hard enough. This is despite doing two workouts per day, at least one of them quite intense. Workouts it used to mark as high aerobic it now counts as low aerobic.

Should I just manually override the max HR or is it possible the watch auto adjustment is accurate and I’m just a slacker? Using the Tanaka method my max HR would be 178. Thanks!