I was using the timer because I was trying to get a photo of myself and the remote was firing the camera but not the flash. I still suspect a bug in the camera. I updated the firmware but no change. If I just press the shutter button OR use the timer it works every time. Just not with the remote. I'm also using the XPro-P, V1, and AD200 Pro with an additional optically triggered speedlight for the backdrop.
This setup is one that I have used many times but without the remote. I use the remote almost daily landscape shooting so I know that is reliable too. I really think it is connected to being triggered by the remote which I agree is weird. But software bugs can be weird too. I'll try some more test to narrow it down more tomorrow.
I used the 12s timer and got the shot to show off my home haircut.
I'm curious if anyone else can try this, even with just a camera mounted flash and a remote to see if you get the same results.