Even very, very shallow slopes, and regardless of whether you are walking or running, you cannot jump. It seems like the problem is that as soon as you jump the game thinks you should be landing and so stops your jumping motion.
This is especially obnoxious in Xen, where it can prevent your long jump module from firing. I died multiple times walking off ledges while trying to activate long jump because there was a slight lip, and I died multiple times on the first phase of the Gonarch because I couldn’t long jump away.
Since realizing the problem I can work around it, but it’s still really annoying.