I reset the Cache allocation from 170Gb to 150Gb ton ensure the drive would not fill:

The allocated cache space of 150Gb is close to filling up again (147.9Gb). Of the total usable disk space of 238.47Gb there is 85.25Gb unused. So the actual drive itself still has free space available.
“ADATA CACHE DRIVE” in disk manager:

Where data is on drive:

I am still receiving this message:

If the cache should automatically overwrite old cache files making it unnecessary for me manually empty the folder, then why am I still receiving this message given that the drive itself isn’t close to being full?
I’ve searched online for people with a similar issue, or settings to control the cache folder auto overwrite but haven’t found anything. It would be helpful not to have to trash all of my cache manually every time it gets close to being full.