I don't know what triggers this, but happens quite a lot, it's not the first time. Some minutes ago it was perma stuck at the vendor trying to repair red gear, it succesfully sold the trash/white items (in facts bags were empty) but it was unable to repair the gear. I waited a bit then I gave up since it was in a endless loop, I close the robot and started again, and it worked for some reason.

I already wiped the NPC database and I added manually every repair npc in my grinding profile, also i removed the "auto add npc to database" and similar options, so basically im using a grinding profile made by me with only 1 vendor (added by me again), so the bot shouldn't go wrong.

Here is a piece of the log

20:21:46.688 - [ToTown] Go to vendor Humphry (Repair)
20:21:47.241 - [ToTown] Vendor found Humphry
20:21:47.241 - [ToTown] Repair items
20:21:48.272 - [ToTown] Sell items (try 1)
20:21:56.422 - [ToTown] Go to vendor Humphry (Repair)
20:21:57.037 - [ToTown] Vendor found Humphry
20:21:57.037 - [ToTown] Repair items
20:21:58.067 - [ToTown] Sell items (try 1)
20:22:06.269 - [ToTown] Go to vendor Humphry (Repair)
20:22:06.807 - [ToTown] Vendor found Humphry
20:22:06.807 - [ToTown] Repair items
20:22:07.819 - [ToTown] Sell items (try 1)
20:22:15.990 - [ToTown] Go to vendor Humphry (Repair)
20:22:16.518 - [ToTown] Vendor found Humphry
20:22:16.518 - [ToTown] Repair items
20:22:17.521 - [ToTown] Sell items (try 1)
20:22:25.722 - [ToTown] Go to vendor Humphry (Repair)
20:22:26.236 - [ToTown] Vendor found Humphry
20:22:26.236 - [ToTown] Repair items
20:22:27.249 - [ToTown] Sell items (try 1)

Any ideas about what causes this weird behaviour?

Hello, it is in vanilla? if yes wait next update. If it is not in vanilla you get this problem with all repair? do you have try to disable wow addons? 

It's WOTLK, doesn't happen everytime, and apparently there isn't a rule, some vendor may work, some other don't, I should do tests and see if I can spot a rule.

But I noticed another thing, I don't know if I'm missing something or what, I created a grinding profile let's say 1-15 divided in 3 zones (example)

Zone 1: Level 1-4, Repair "A" added in NPC

Zone 2: Level 5-9, Repair "B" added in NPC

Zone 3: Level 10-15, Repair "C" added in NPC

Happens that it changes correctly the zone and the grind path based on the level, but when it needs to repair, if it is in Zone 2, he goes to Repair A instead of B (which is obviously closer that's why I added it). Now every vendor I added has every "check" (Can fly to, save, current profile active), should I mess with these checks to force the bot to use the profile npcs i added? Also, do I need to clear the NPC database each time I use the grinder? I already disables the automatic add of nearby npc and still it goes to other vendors that I didn't even add. It's kinda confusing, at least for me. Can someone explain better this stuff?

EDIT: No I didn't try without addons, but I don't use anything special, just "cooldowns" to see the seconds remaining on spells on cd,  and "power auras"

I noticed sometimes (on long sessions) it bugs and keep opening the vendor and closing it without selling anything. If I restart wrobot the problem goes away and it immediately repairs and continue the profile.