Hello Anton,
The maximum number of loads and requests that can be processed simultaneously is defined in the table SMOFPARSFA under the MAX_PARALLEL_PROCESSES..The hierarchy in order of preference is initial load, request load, and then SDIMA.
There's no harm in updating the MAX_PARALLEL_PROCESSES from 5 to 10(or even 15 if your settings allow it).
For the rogue entries you see in SMOFRSTAT, just check the date these request loads were initiated.
If they're very old and there's no associated queue you can find for them in CRM/ECC you might as well set their status to DONE(after editing the table manually).
Regards,
Rohit