No, it's not normal. Something like this sometimes happens in mountains when there are lots of requests on terrain tile generator, and internal limits for terrain tile cache are reached. Looking down can help in that case, as remote terrain goes out of view and can be reused for nearby tiles. But this doesn't happen on most of the land, and it self cures when you move to a less demanding location.
Please go edit eng.cfg and set debug_keys = true there, and then when you experience this issue, press alt+5 to show tile stat window. Might be that with debug_keys it will pop up by itself too. Just make a screenshot.
I didn't see any injected modules in the log, but there still may be some hidden - are you using any kind of graphics utility, for things like capturing video, screenshots, displaying fps overlays or any similar thing?