I've been rooting this way for longer than I've been alive! ;)
I wait until the roots are ay least 1.5", more is better. If the roots are turning yellow I'll poke a few holes in the bag to make sure they don't rot. If they're headed toward brown I get the cutting out and in to soil. I pot into promix HP with bio-myco moistened then squeezed out and fluffed up. If you're using minimal moisture in your potting soil then I wonder if it's the way you unpot then repot. I do one of 2 things. If I have an individual cutting I slit the bag while holding it upside down. The roots are stronger in this position and less likely to break. As the bag opens up, perlite slowly falls out and just the pieces stuck to the root are left. That way there's less weight hanging on the roots. They go into a pot that's already waiting for them with moist pro-mix in it. The soil looks like a bowl with the bottom of the soil about 2 inches from the bottom of the pot. I hold the cutting in place and gently let the soil fill in around the roots. I do not tamp the soil down. The roots need those air spaces in the soil to survive. For the first few weeks I either water it from the bottom or use a spray bottle to water it from the top. Both of these methods preserve the air spaces in the soil.
If I'm doing a mass rooting in a sterlite box with holes drilled in the bottom then I put that in a bigger box, run the hose over the perlite and keep the box with the cuttings submerged. The perlite will float en masse, taking the cuttings with them. I scoop off the perlite that floats free and keep doing this until some cuttings float free (they turn horizontal.) I get all the perlite that's floating free away from the cutting so I don't pick up any excess weight. I support the cutting and lift it out. I never touch the perlite stuck to the roots. It goes right into the pot with the roots and will help provide air spaces. I have the pot waiting just like in the other scenario.
I bury the whole cutting in perlite except the very tip is always visible. I do not use a humidity dome. That way the leaves bud out into dry air and they're used to it from the start. No transitioning needed and no plant loss from leaves that couldn't adapt quickly enough.
The bio are beneficial bacteria that eat the pathogens that thrive in overly wet, air deprived places that rot roots. The myco are fungi that combine with the roots to make them more healthy. I think they're very important.
One of the crucial things about perlite is that you have to get rid of the dust. If you don't it will cling to the cutting, attract water and drown the cutting. I usually rinse through a colander to minimize dust.