This! The sample you show looked a bit loose. Another trick I've learned is to make casing solution with some saddle soap, it really helps to lubricate the surface and allow for cleaner/smoother more controlled cuts. Give it a try. Also, sometimes I'll run a glass slicker over the surface a bit to help even the compression of the fibers. At any rate, after I've cut for a bit, almost inevitably material builds up on the blade and I will begin to feel a bit of drag, so strop again... and again.
Casing solution done right can help prevent any mold forming. I live in a very humid environment, and have had work on the bench for days with no issues. Heck, the first thing I ever tooled got interrupted by a hurricane, stayed in a zip loc bag with no air conditioning in hot conditions for over a week before I could come back. It is now a 3 ring binder with an eagle. Do some experimenting with scraps to see if you have any issues.