First of all thank you for this amazing mod.
I've been using it without problems for a long time but with my latest pyanodon game I'm having huge issues with the search. It started fine but searching has taken longer and longer up to the point where the game basically freezes for 10 seconds after each letter I type in.
I have been using FNEI extensively this game and since it's getting gradually worse over time I was wondering if my gigantic search history might be causing this issue. Any idea what I could do? is there any cache I can clear or an option I could disable?

I'm still playing on 0.17.74. Updating to a newer version is not really an option since the MP server I'm playing on is running this version.

I have found a workaround for anyone running into the same issue:

1.) Disable FNEI and load your latest save after the game restarted
2.) Save your game with FNEI disabled. This reduced save file size by 2.5 Mb for me!
3.) Enable FNEI and load the purged save file.
-> FNEI search runs perfectly smooth again.

Looks like the gigantic search history was indeed causing the performance issues.
@npo6ka: maybe consider adding an option to not retain search history (or limit it's length).

This seems to still be an issue. The quick fix posted above works fine, but it needs to be done quite often. Is it possible to add a mod option to not save the search history? Or maybe limit it to 5 or 10 last recipes?
Alternatively a button in the FNEI GUI to reset your search history?

Would help a lot :) Thanks for a great mod though!

Problem is still an issue, just had to apply the fix above to make it usable again. Why not just save the history in-memory only, there is no good reason I can see to persist it in saved data.

Especially on my slow internet connection this induced massive lag spikes in modded multiplayer games

Not one of my issues but i saw an unreported case:
https://www.reddit.com/r/factorio/comments/n38hra/am_i_the_only_one_who_has_fps_drop_while_using/

He had FPS go from 60 to 20 when clicking a recipe in FNEI, and disabling mod "Improved Research Queue" fixed it.