Welcome to the world of memory tunning.
XMP/DOCP/EXPO are all a form of OC and not the guranteed speed you might actually get. Not because of the CPU IMC alone but also the board QVL among others things like silicon lottery.
I would start by using the DOCP profile but tweak out some values. Loose the values of the 4 main timings and be sure to put comand rate 2T. Maybe you can get back to 3600 stable.
OR
Use 3200 with agressive timings, It can be as good as 3600 loose timings.
Good luck
The Englishman