I have that now... except my fall back seems to almost always happen the day after my temp spike (2 DPO)
April - Temp spike 97.7 The day after 97.3
May - Didn't happen, but May was a jacked up cycle with a 9 day LP.
June - Temp spike 97.7 The day after 97.5
July - Temp spike 97.78 The day after 97.77 (okay that one wasn't bad.)
Aug - Temp spike 97.92 The day after 97.71
Nothing was ever "wrong" any of those times... except for May. I dunno what May was about.
So apparently, that's "my" pattern... to fall back at 2 DPO. Maybe your pattern is to fall back at around 4 DPO.