I've been having similar issues with the stuttering. Once the stutter starts it persists even out of game in desktop(in VR). The Stutter seems to start when something graphically demanding changes in game like turning on a TV POD or low level with ground detail being viewed etc.
Last night when the stutter started and pretty much locked up the game, I clicked pass-through mode on the Rift S controller and then went back into the game and it was instantly smooth!
This seems consistent with what other people are doing alt enter and such - Maybe this is somehow resetting the HMD within DCS.
I only play multiplayer so don't know if this would happen in single. I believe this to be a DCS issue as I've never experienced it in any other game.
Best way to solve most issues like connection and tracking etc is to have a powered USB hub for the Rift S. Worked for me anyway.
Update - It seems this might be more related to ASW turning on despite using the tray tool to turn it off. I manually turned it off mid stutter with oculusdebugtoolCLI, using command "server:asw.off" and this did work for me.