I was on one of the Early User Assessments (EUA) when I was active duty, and then when I got out I served as a New Equipment Training (NET) instructor for the initial fielding to all the units. The L & H variants were particularly hard on most of the optics at the time, but most of the SOPMOD block II optics and later were tested and beefed up to handle the weird recoil profile. Shooting suppressed helped quite a bit. The H with the short barrel unsuppressed was particularly hard on optics.
It’s probably common knowledge at this point but the L variant fell out of favor with the operators pretty quick. The H is still in use for some units for certain roles, but not as prolific as one would have hoped after so much money was spent on them.