How many rules in total do you have? Also, are you running any other scripts in parallel with the looter?
I have seen sometime when loot time increases as run time also increases, but not nearly what you're experiencing.
The real only thing that we have control over is the size of the variables that are accumulated over runtime. You might want to take a snapshot of your vardump (Tools/VarDump) when you first start the script, and then take one when you start experiencing slowness. Then compare the sizes (in bytes or lines) of the 2.
It's been a while since I did an analysis like this. Feel free to PM me your results, but don't post the actual vardumps because there's account specific information.
Also, there's an older version still posted. You might want to try that and see if it works differently.
Thanks for your reply, TM. I'll try using vardump before and after running the script for a few hours. I'm also running another script that calls CLAW to check loot. Additionally, I'll test an older version to see if the scan time increases over time with that as well. Actually, I noticed this issue a while ago, but since I wasn’t running it for long periods, I just lived with it until now, lol.