Finder tags not working with external drive

I'm archiving my old photo (analogue) collection with my Epson FastFoto Scanner & it's amazing most of the time. But the ones that have dark backgrounds or are underexposed etc create huge issues. I'm unsure whether it's JPEG artefacts or noise.

I tagged the images I wanted to go ahead and rescan via ImageCapture on my printer. I tagged them (with the colour tag thing, but with a custom tag, not a colour), and they just disappear. The images are still on the external drive, but nothing shows up when I click on the custom tag in Finder.

I thought the tags disappearing from the images was a one-off as I had decided to convert the images I'd scanned from TIFF to PNG via Automator to save space, and started going through the actual images (I separated them from the main images, but I'm anxious I messed up somewhere and missed a few and am a perfectionist which is putting me off going back to look at them or trashing all the digital images to start again, again).

I came back to them after a week or so and suddenly, none of the images I'd tagged showed up (I've scanned a thousand images, so probably tagged maybe 150-200?) when I plugged the external drive in now. I just tested it and picked a random image and added the custom tag, and it showed up under the custom tag and then disappeared when I removed the custom tag (which I expected). Any ideas on how to get the tagged images back without having to sift through 1000 images again and/or why it's doing this?

This is a BRAND NEW 2021 MacBook Pro 14 inch (MacOS Monterey) with an M1 Pro chip and standard storage and RAM. (less than 1-month-old; I'd been meaning to work on scanning my photos when I upgraded to this one from a 2016 Touch Bar but not its causing issues) Even though I'm not 100% sure I used tags on my old MacBook Pro, I never remembered it doing weird things like this.

I don't want to have to do this every time, and I guess I'm lucky it's 'only' 1000 photos and not say 5 or 10 or 15 thousand, but its still very frustrating.

I tried reindexing Spotlight three times. First time nothing happened, so I thought I did it wrong. Then I followed the directions directly on Apple's website, reindexing Spotlight for the external drive itself and the folder within the external drive where the images are located, but neither worked at all.

Help please! I'm seeing a few Apple discussion forums with this issue, but none related to MacOS Monterey.

The only real possible solution I've come across is reformatting the drive from EXfat but I find it strange that it worked briefly, and I'm not sure how much space I have on my other external drives to move everything before wiping/reformatting and moving back.

Is formatting from EXfar the Mac journal the only option and will it get the images back which were tagged before? (the images are still safely on my drive, but it would make it so much easier for me to have the tags back so I wouldn't need to go through 1000 photos and individually tag them and then find the physical counterparts, I can just search the tagged images and check the photos I kept aside.