OOTP league files for larger leagues can easily exceed 300MB in size, and in some cases, can even get to 500MB. This causes issues with upload and download times, and reliability in general.
One easy option to reduce the file size is to have OOTP exclude the faces.dat file from the league file. This file can be up to 2/3 of the overall file size, and isn't required. Although some GMs may not see exactly the same player faces, excluding the file saves a lot of trouble.
To exclude it, use the "League File Settings" dialog from the automator:
On the next dialog, uncheck only "Include faces.dat". You will definitely run into issues if you don't include names.dat and retired.dat, so always include names.dat and retired.dat.
Also recommended is to set "Messages from past X days" to zero, so no GM ever misses important in-game news. For box scores, game logs, and replay files, use a setting 2-3x your usual sim length.