Face Recognition quality

It is not possible to reset face recognition without losing all of the face recognition already performed.

I don't understand why you are having these problems.  If you have had every version of Elements since day one, and have always had face recognition turned on, why do you now have 25,000 unrecognized photos/faces?  Do you mean that you have just imported thousands of new files into the catalog? Or have you started face recognition again?

I have nearly 200K media files in my catalog and I have been an avid user of face recognition which I believe started around version 9.  Several months ago, I rebuilt my catalog and started face recognition from scratch.  A lot of my photos are from my grandkids' school events/concerts.  So there are many recognized faces that I have no need to name.  In my experience, Elements 2021 has much improved performance, both in terms of accuracy and speed.   I ended up with  several stacks of my close family members, containing over 1,000 faces in each stack.  And for the most part, once a name was applied to a stack, it would be regularly auto-completed in the next stack of the same person.  I probably had over 40,000 stacks to name, but using the tools available, I was able to complete the project in 2 to 3 months.  Some of the techniques I use are:

• hide the side panels so the screen shows more stacks
• scan through the stacks and multiple select the false positive faces (what you describe as sections of walls, floors and sky etc.) to use the Don't show again controls
• use Ctrl-Click, Shift-Click and Ctrl+Shift-Click to select multiple contiguous and non-contigous stacks of faces for naming or removal
• name all recognized/wanted people stacks until a group of unwanted stacks appear, then shift-click to select all stacks remaining on the screen to use the Don't Show Again button
• alternatively, select and remove all unwanted faces until a full screen of wanted stacks is in view, then name them
• when down to small stacks, scan for a particular person's stacks, select the stack with a Ctrl-click and then use the Merge People button to combine the stacks

And if Elements doesn't correctly recognize the name for a stack, it usually only takes the entry of one letter in the text box to bring up the correct name for auto-completion.