AH!
I just realized something I missed from the OP: "schedule.txt has less than 7000 lines".
I make most of my edits on CM16 (which changes the compdata files when I save), and my schedule.txt is at just over 7,500 lines!!! (7,571 to be specific) THAT must be my problem at the end of the day!
The problem is that I don't know exactly WHAT to cut from it (actually I do, but I'm really indecisive - I'm thinking of cutting Austria and Ireland, which I think are pretty useless, but they don't amount to the total I need to cut out). Does anyone have tips?!
EDIT: Trimmed Turkish League's calendar (actually pasted Bundesliga's calendar onto it, which had less unnecessary dates for the same number of teams), and that pared it down a bit, but it still didn't get there (currently at 7,446).
EDIT 2: I've been thinking, and I decided Poland would be my third cut. That brought the sum of lines cut to 471, 25 more than I need (111 from Austria, 101 from Ireland and 259 from Poland). I adjusted the European competitions accordingly (I didn't delete the leagues BTW, just the competitions, so they aren't playable in Manager Mode), and also took out some unnecessary legs from some other competitions. Current line total: 6,984. Now to test it.