Jumping occasionally takes too much fatigue
I've mentioned this once previously in another issue but it was dismissed, so I'm opening a dedicated issue for this.
As the title suggests, fatigue cost of jumping is not consistent in OpenMW. Sometimes it's the ~5-7 as in Morrowind, and frequently it takes away huge chunks of your bar, up to 20-30 per jump.
You can test this with a fatigue restoration item such as the Darksun Shield. With 10 points like from this shield, it is not possible to deplete the fatigue bar with normal jumping in Morrowind, at least with maxed stats and 400+ max fatigue. Only spamming jumps when moving up hills or stairs can use more fatigue than generated, and this isn't possible in OpenMW (yet, hopefully, but that's another issue). In OpenMW you can still quite easily deplete your fatigue bar even with the Darksun Shield equipped and maxed stats.
I've once read somewhere that the stamina cost of jumping in OpenMW is dependant on your ingame framerate, but that's just what I've read. I do not know the cause of this issue.