It's a sign that you should get to level 3.

This section, a short uphill trek to a ruined bothy remains a sublime moment seared into my brain years later.

Thanks to the Serious Sam Wiki for the screenshots.

It's hard to say without having the build to go over. Personally I'd throw up a crash report for catching leaks. But also knowing how quick the turnover is on these types of games I can imagine just having it run was the goal.

That build probably has a memory leak and its default response to memory getting too filled is to deload textures and cull really aggressive.