Did you try putting in 64 gb?
Spreading the word, I got higher than 32gb working installed on my 2013 27in.
With Catalina it will probably work on 2013-2015 Imac's
iMac 27-Inch "Core i7" 3.5 Late 2013 Max RAM is higher than 32gb
My wife has had a "Late 2013 27in Imac" for 6 years and does print design on it 24/7. It's been getting long in the tooth and I've upgraded it over the years with an SSD and added 32gb of ram a few years ago which it regularly maxes out through Photoshop. We were debating getting something new...forums.macrumors.com
I had to pull them but my IMac is fine, it could recognize the amount but didn't work well after a few hours. 2014/2015 would be the next one to test since the CPU are more recent, I think Intel has done some microcode updates that may make it work. Plus I never tried Windows 10. There's some stuff to be explored still.I saw the thread. Did you almost brick the iMac and had to pull out the extra RAMs?