I have tried the slot adapter in all of my other Slot 1 motherboards (incl. VIA and Ali chipsets) and NONE of my CPUs work in any of my motherboards (even the Mendocino Celerons don't work).
Here is the adapter that gives me problems (I couldn't find it on the internet, only the Pro version with the jumpers, so I uploaded a photo of mine):

I am either doing something very wrong here or this adapter is broken. From a visual perspective it is flawless (no scratches or damaged traces). It just refuses to work.

Time to start hunting for another slotket then - having several is almost a must when you are into playing with Slot 1 motherboards anyway.
One suggestion... it would be a good idea to find versions with a housing to hold them in place in the brackets on the motherboard. The 1.1Ghz/1100Mhz fsb 100 cpu's are the hottest of the Coppermine family and the kind of robust cooling solution that they need may be too heavy for a slotket that just hangs in there by its gold teeth.

Strange that the GA-6R7 doesn't work with any of your cpus - v1.1 (late 1999 / early 2000) was qualified by Intel with the GA-BX2000 and the GA-6BX as supporting Pentium III processors in FC-PGA package. I've never had any such issues with mine (v1.7). I'd just pick up a MSI MS-6905 Mater, cheap off the Bay.

Do you have the latest BIOS installed?

Currently using P2B-S with P3 550E Coppermine and MSI GF MX440. The system works flawlessly with 98SE (in fact I never had such a stable and compatible Win9x system). It runs all of my games except NFS SE, wich is a PITA to get running anyway. The performance is ok so far, but it makes me wonder why I can't get that adapter working. I remember it running once with a Mendocino last time I used it a few months ago.

TechieDude wrote on 2020-04-14, 16:03:

Do you have the latest BIOS installed?

Yes, 1014 BETA.

It may sound silly, but you might as well try rubbing the contact pads of your slotket with an eraser. I've fixed a lot of "dead" DIMMs that way.

TechieDude wrote on 2020-04-15, 21:07:

It may sound silly, but you might as well try rubbing the contact pads of your slotket with an eraser. I've fixed a lot of "dead" DIMMs that way.

I tried it, no difference.

computerguy08 wrote on 2020-04-17, 20:06:

I tried it, no difference.

Which part of the eraser was it? The red or the blue one?

TechieDude wrote on 2020-04-18, 12:35:

computerguy08 wrote on 2020-04-17, 20:06:

I tried it, no difference.

Which part of the eraser was it? The red or the blue one?

It was green all over, like one of these 😀

Doesn't really matter, the fingers look like they are brand new after the wipe.