Colours in document became muddy/muggy

UPDATE:

Yesterday a warning came up at the bottom of my Illustration window about Pantone colour palettes. I don't know if that has anything to do with anything.

A new version of Illustrator also became available for me yesterday so I installed the new version and the Pantone message didn't appear again. 

While I couldn't replicate the same issue with the same layers from that file, I did continue working on my project in a new window and the issue happened again for this new file with different, newly created layers. These layers were clip art illustrations where as the previous file was pattern layers. As a preventative measure I wrote the colour values/numbers next to each layer to keep a record of the original colour numbers/values and they had changed while I was working on the file. I worked on that file for 8hrs yesterday, saving as I went along. I took a break twice (around 1hr each time). I notice the change after 8hrs. I had also saved a skeleton file initially of the first few layers I created that I would be working with and making variations of, when I compare the two files I can also visibly notice the changes in colour. The colour values/numbers I wrote matches the skeleton file version but did not match the colours of the layers from the file that I worked on for 8 hours. 

I replaced all the colours of the layers in this file to the original colours and copied and pasted the layers into a new file. (Just in case the file was corrupted (I don't know...I'm just clutching at straws at the moment)). 

This is everything I have done up to this point. 

It's is Mac OS version 11.7.10. Big Sur. My Mac is up to date for the model that I have (Retina 5K 27-inch, Late 2014).

I have only one monitor. 

The files that I took layers from both have the same document colour settings/mode. I dragged the layers rather than copy and paste. 

These two files are 2 years old and 3 years old, respectively. They are sort of a 'master file' of design templates/layers that I tend to re-use so I drag pattern and shape layers from these two files whenever I am working on something new and want to reuse some of those layers. 

Document Colour Profile: sRGB IEC61966-2.1

Color Profile: Working RGB: sRGB IEC61966-2.1

Colour Setting: Custom

working Spaces - sRGB IEC61966-2.1

Color Management Policies - Preserve Embedded Profiles 

Conversion Options - Adobe (ACE)

I hope I've listed this correctly.