I bought the Hornet module over the weekend (Steam version, if it matters) and I'm seeing this behavior as well, in addition to some other odd quirks. Frankly, given how much the modules cost, it left a pretty nasty taste in my mouth - enough I almost returned it.
Here's what I'm seeing:
1. It seems that I have to go delete the metashaders/fxo files EVERY time I want to play the game, or I get horribly low framerates whenever I look forward. Subjectively, it seems like maybe it's related to the HUD, or some other instrument in the cockpit, as it gets a little better if I look to the left or right.
2. The problem comes back, deleted metashaders/fxo or not, after I land the Hornet. Again, it's the worst looking forward through the HUD, and mostly goes away if I look away.
Hardware in question:
RTX 2080 Ti
Core i9 9900K
16GB of memory @ 3000MHz
HTC Vive Pro
Settings in SteamVR are the defaults. Settings in DCS are basically just the VR preset, but with all the shadow settings turned down to the lowest option.
Edit: I didn't have a ton of time to troubleshoot this, so I can't be 100% it's limited to the Hornet, but the only thing that changed over this weekend, as far as I know, is that I bought the Hornet module, and I've never seen it do this in any of the other airplanes.