Slowing down after multiple searches

I've noticed (though haven't actually measured the times) that if I am doing multiple searches for duplicates amongst several thousand files, it pretty fast for the first search but subsequent searches using the same initial folders plus some additional ones is slower. This is barely perceptible for the first 2 or 3 searches but eventually it is markedly slower. Re-loading the program doesn't help, but re-booting the PC then re-loading Opus does. Is this my imagination or am I losing memory assets as I go through the searches?
If the latter, is there any way of freeing up memory without having to re-boot?

What does Task Manager show is happening?

Which columns are shown in the Duplicate Files results?
And is thumbnails mode being used at all?

Which types of files are being found (e.g. video files)?

PC has been on for some time and has run a few searches for duplicates, Ran a search for duplicates in two folders located on separate discs - a oldish USB2 external disk and a new USB3 external disk. Took around 11 minutes. A run post cold re-boot about 30 seconds faster.

Task manager - shows Opus, Chrome and Task Manger running plus over 100 processes. CPU running at around 5-6%. Memory 26% (of 16Gb).
Columns are Name.Size, Type, Attributes. Modified, Location. Files mainly JPEGs, no video.
No thumbnails

How much memory does Task Manager show Opus is using? Does the amount increase as you run different searches?

I'll try out a few different searches and get back to you. May not be until end of week though.
Thanks for addressing the issue.

I think I may have wasted your time on this - apologies.
I could not see any significance change in memory use regardless of search. What I have noticed however is that the cause of slow appears to be when it finds a folder containing large files searches. The majority of my folders contain JPEGs, but scattered amongst them are batches of TIFF and RAW files. These two seem to be the cause of the slow down ... and the old adage of watch a pot never boil!