I recently notified the SIG Customer Service Team requesting to exchange the original grip module from my brand new P365XL due to an excessive amount of front to rear movement of the FCU within the module. The CS rep indicated this slop was normal for the P365 (as well as the P320) though offered me an opportunity to return the pistol for evaluation. Since I knew from prior experience the nature of the problem, I elected to not return the pistol but rather purchased an accessory grip module on my dime. I'm pleased to report my FCU now fits snugly within the new module and displays zero front-to-rear movement. Has anyone else experienced excessive movement with their P365 (or P320)? Thanks!

No on ANY excessive movement with all of my P365's and P320's. In fact, all of them fit kinda snug.

Isn’t there a pin that you have to drive out that prevents forward and backwards movement and locks it up tight??

No on the 320s or on a 365XL.

None of my P365s or P320s fit sloppily, and they are all FrankenSigs that I built around standalone FCUs. One of my P365X/XL grip frames is however, a bit tighter than the other and takes a bit of effort.
Sounds like you might have drawn an out-of-spec grip frame from the factory, which is not beyond the pale with Polymer. Should have been caught during assembly. I've gotten Magpul AR grips that were either loose or too tight to even install.

My one and only, a recent 365XL is perfect in that regard.

Update - I spoke with a different SIG CSR this morning. After explaining my concern and forwarding a photo of the inside of the grip module, SIG has agreed to send me a replacement under warranty.

Yes, going through something similar as well. The oem grip on mine had up and down movement and rattled badly if I shook it a bit. It did shoot fine but this was annoying. I bought a Wilson Combat grip and it's tighter then a drum. I exchanged emails with Sig CS, and as with you, the offered a return tag but I'm not wanting to go through all of this crap and might buy a new oem grip module and if it fixes the problem I'll get back with CS and see what concession they can make.

I'd just stick with the WC grip, but my wife occasionally likes to shoot the gun and prefers the thinner, smoother oem grip.

This is not the first time that SIG has these poorly trained CSRs pull BS answers out of their asses. Truly embarrassing.