OP
I don't think you can't tell an ACL is LAX by "how it feels" after a ride.
You need an IMAGING STUDY- MRI probably.
Diagnosis from physical exam-even from an expert-is WAAAAAAY inferior to an actual imaging study.
6 months of no bike-absurd-
You need an actual diagnosis based on imaging study-not just a physical exam.
I really question their competence-6 MONTHS?? -no mention of MRI ???
Like I and other have said-YOU DON'T NEED AN ACL TO RIDE A BIKE
I haven't had one since Nov 1968- heck wrestled 5 more years -college-without it-ridden almost daily (except 1983-1998) since 1968.
Riding will STRENGTHEN you leg muscles
Now probably good idea to do some Hamstring work(leg curls) since biking is mainly quads-

Safe bet you are over training- a couple of weeks off would do you some good-then drop your miles-add some leg weight lifting - hamstrings
6 months -no MRI- is just BS-
You are over training- take off a couple of weeks-drop miles do leg work for hamstrings

Bike riding causes over use injuries-it doesn't tear ACLs (unless you crash)
It is a pretty narrow range of motion-not like a deep squat-so it isn't going to loosen your ACL-