Also seeing these dips and I also thought it had to do with spawning... at first.

Can you try these things and report your results here?

Turn off SSAO - does this fix anything?
Turn on SSAO, but drop shadows to lowest... how is this for you?

When I turn off SSAO 98% of the game runs @60FPS, but looks terrible... (using a GTX1080)

When I turn off the shadows (lowest) and turn on the SSAO, I'd say about 85% runs @60FPS

Technically the game runs at 60, but yeah... these drops. Anyway... for me they become less frequent when messing around with SSAO (not a valid option) or the shadows.

I decided to go for the second option... game still looks good, but runs smoother.

i already had SSAO off so i tried turning it on & my fps dropped by 15 or so. tried turning point light shadows & shadow quality to lowest and noticed no difference. though i am also using a fps mod that sets shadows to 0 & adjusts a few other things to very slight boost my fps. my graphics card is a gtx 970 so its a bit older than your's.