After completing the quest by killing Olmu Llendu outside of Necrom (did not test other outcomes), Laalalvo Irano will not provide the player any new quests. Each time a topic "orders" is selected, Irano will tell the player the same line as at the beginning of the "No Sin Goes Unpunished", that is to kill Olmu Llendu again.
Our old iron ore ingredient was replaced with T_IngMine_OreIron_01, and I don't think its placement has been corrected since. There are lots of floating and/or bleeding iron ore pieces in mainland now.
During TR_m3_OE_GhoulBusiness, if the player finds the corpse of TR_m3_Tindalos Miranus, TR_m3_Galug the Barber is moved behind the player, with the intention of triggering a ForceGreeting when the player approaches him. This works, if the player has visited Ebon Tower, Mara's Tower where Galug is normally located.
Port Telvannis riverstrider port has a main entry door that does not open/animate when activated, and does not show flavor text indicating whether this is intentional. I'm not sure if it's a Tamriel_Data thing or a Mainland thing since it seems to be a script issue.
UPDATE: Confirmed by Atrayonis to be an OpenMW physics conflict with slaves colliding on slave market cage geometry, should be fixed in OpenMW nightly. (March 27, 2021) Hemaris and Minerman60101 note that the lag spike may also be caused by the slave market itself, as disabling the holding doors, cell doors, and ex_t_root_04 reduced lag significantly due to collision calculations.
The Imperial Legion quest Properly Purloined sends the player to guard the sewer entrance to the Ebon Tower's Treasure Chamber. It is a low level quest where you end up killing a couple of rats and dealing with a thief. However, the key the player is given to access the sewers allows them to easily access the treasure chamber and grab some very nice loot, such as the Cuirass of Cassynder Septim, with little effort and no consequence.
The molecrab under the table in cell Aalmu Ouradas' Shack plays its death animation the first time you enter the cell. Its refID ends in "molecrab_dead" so I assume it was supposed to be dead already before you got there.
I should specify that I saw this in OpenMW 0.46.0, in case this bug is due to an engine limitation. But I played through the Bloodmoon MQ (with TOTSP installed) on this same build and didn't hear any dying horker sound effects during that part of the questline, so I bet there is a way to fix this.
The lower platform in Galseah, Deep Caverns is missing a ladder, making the npc followers from the Avenge the Knights quest get stuck if you lead them down there, and the enemies there unable to chase you up the stairs.