Framerate hit when not in PIE, also after 4.12 to 4.17 conversion

Okay so I’ve been working on a passion project for ages in 4.12 - and now that there’s the Spring Sale, I was thinking of moving to 4.17 to take advantage of the assets there.

But immediately after the conversion, it seems like I’m going from around 120 frames per second to somewhere around 30 frames per second.

I edited the Project Settings to clamp the framerate to 60fps … → (see attached picture)

but that only seems to work in the PIE. It’s smooth again in the editor but is low again when outside of it.