Agree there is no link established (yet) with any known cause for MGUS, but human nature is to try to do what we can to feel in control vs feeling helpless.
I have questioned links with vaccines, weight/diet and stress levels (chronic and/or acute trauma).
I had to have the rabies series shots and immunoglobulin treatment recently (tried to pet a stray dog in Turkey that bit me!) and m protein remained too low to detect. But FLCs went up. Will recheck in May but maybe it will return to baseline.

Also, I have discovered a connection between stress and FLCs and found it does increase during physical and psychological stress. I experience increased thirst and slight bubbles in my urine that last a few hours before returning to normal when I feel anxious or stressed about something.
I try to be more aware of my stress response and include relaxation practices- hope this was helpful!