If you used a video inspection and found nothing amiss, then the next best thing is to have your licensed plumbing contractor use a “retriving” head on your next stoppage. This will bring back the cause of the stoppage (hopefully).
A lot of times it is something as simple as a pamper/sanitary napkins that can cause severe blockages.
You many also want to find the exact place the blockage occurs as this could be either an improperly caulked joint (Cast Iron Bell and spigot) Or possible pipe settling which can cause a slight belly or back pitch.
Depending how often this happens you may want to have this system hydro jetted once a year to remove possible grease build up from washing machine and kitchen line discharges. Preventive cleaning
( NO DARN Chemicals) If Anyone pushes chemical treatment RUN LIKE HELL from them. Good luck
SylvanLMP