Yes, I've increased to 6-7-8 task limit, but I'm not sure that repository can handle this. I hope so
Anyway sometimes It could work but when I'll add a new backup job to backup copy with 3-4-5 vms inside it, I'll be back in the same situation.
Clearly, after first full, slots will be free in a short time so the problem is not so serious
Maybe 9.6 could introduce priority feature