There was some kind of change after ModularMachinery-1.12-1.7.1.jar that makes it so you can no longer hold the 3D models from flans mod without your entire screen, minus HUD, blacking out. Reviewing the commits didn't tell me much so I was just hoping the devs could offer some insight.

This is a flan's issue, as it happens with more than MM. A lot of mods, actually. Sometimes just Forge. They have some weird rendering code, and their GL conflicts with a LOT of things. This hasn't changed since this particular issue was discussed in 2018 in Discord.

I do see you commented on FlansMods/FlansMod#959 however, so linking it here for cross reference.