This may or may not be an issue, but I changed my decay setting from optimal to small decay and back to optimal and only noticed a change of 1w in my TP between each setting. Is this a bug or expected in some scenarios.
I wanted to update my TP to reflect where I am with training as I have a 20w difference vs TP and what I expect my TP to be at based on recent training and efforts (Not BTs).
I’ve adjusted my power curve based off recent efforts to correct and now it seems accurate.
When you change decay settings, Xert will (by default) recalculate your data using the newly selected decay method starting from your last breakthrough. If it’s been a long time since your last BT, you’ll likely see more of difference in the decay settings.
As an example, I have been at Small Decay so far this year with my last BT two months ago.
Due to that gap, I got the pop-up warning on XO to change to No Decay. When I approved that my signature recalculated and jumped 15 watts in TP, one full pt in HIE, and 20 watts in PP.
All of which I consider legit based on how I have been feeling, performing, and the number of PRs recently achieved on Strava segments including numerous top three entries for my age group (70-74) and even a couple top ten Overall spots. Okay, those are for short climbs and 9th and 10th place, but still. 
My TP is within a couple points of what I reached last year at similar TL.
I’m currently at 4-1/3 stars with an IR set to Slow and am about to complete a second Base period for the year. Unlike my first TED which was an arbitrary 120-day target set to mid-Apil, I now have an actual event planned for August 19 (MWARHB). I haven’t done an event like this in decades but if I’m feeling good, I’ll give it my best. Otherwise, I’ll ride as easy as possible for the fun of it. 