I never ran into this issue before updating today to the early access release from the last stable release. I'm losing my midi grid, especially if there are a lot of chopped up clips in lanes, it gets grayed out the more of these transparent guides that stack, not sure how else to describe it. Here is a screenshot with four midi tracks selected.
(edit: found the "clip outline" option, don't know if that just changed when I updated or if something else changed as well)