I found your comment/site when searching for asymmetric weakness. Many similarities in symptoms but a lot more limb issues than you mentioned. Im going to spare you 30+ year history..but when my children developed symptoms similar to mine, my atypical MS diagnosis was thrown out and lots of MD testing on my youngest began. All generic testing coming back negative. FSHD 1&2, multiple limb girdle types. They are now looking into metobolic disorders including mitochondrial disease.
Just a thought. Maybe something worth checking out.
Sorry your going through this. I know how hard it is when you don’t have a name for the symptoms.