Won't Sync

Is there a limit on the number of users that SendPress can sync? I have one user role with 7,562 users that was able to sync fine. But I have another with more than 80,000 users, and one more with 8,533 and neither will sync. In these last two cases the sync seems to stall out and users are not added to the list. I just purchased the pro version but can’t send mail to my users. What can I do? FYI, on my beta site I have already tried disabling all plugins to see if it there was a conflict but it would not work even though it was the only plugin enabled.

https://ww.wp.xz.cn/plugins/sendpress/