Mirror not deleting large folders

[chota300]

I am mirroring one external USB hard drive to another; the drives themselves are identical.
It has been working well for many months.
However, I let the source drive - and therefore the target drive - get too full.
They are not 100% full, but so full that I decided to move some source folders to a 3rd drive.

After the source folders were copied to the 3rd drive, I deleted 2 small folders from the source drive.
Deletion of those 2 folders propagated to the target drive as expected.

THEN I DELETED SEVERAL LARGER FOLDERS FROM THE SOURCE DRIVE.
Deletion of those larger folders did not propagate to the target drive.
No errors were reported in the log.
And rerunning Compare did not detect any differences between the drives,
even though I could still see and browse those supposedly-deleted folders on the target drive.

So I manually deleted the folders from the target drive.

I do not know what could have gone wrong such that Sync thought it deleted the folders
from the target drive but had not.
And worse yet I do not know how Sync Compare still thought that the target folders were gone.

I have manually corrected my drives, but I would like to understand what went wrong
to prevent such a Sync error, especially without Sync knowing an error occurred.

I do have the latest version of Sync Donation on Win 10 64-bit.
The external drives are Seagate 8TB.

Thoughts?

Thank you.

[xCSxXenon]

What are your filter settings?

[chota300]

Thank you. My bad.
Long ago I had excluded these particular folders because they were no longer being updated on the source disk. I must have read right by the exclusion list when I checked the Sync job.
Thanks again.
Very good.
All makes sense now.