Wireless clients endlessly roaming between APs for same SSID

Hi everyone. I've got an odd issue occuring at a client site with some tablets and their wifi system. I'm no expert on wireless, so I was hoping maybe someone could chime in and shed some new light.

We have 6 vendor-provided tablets running Windows Mobile (6? 6.5?) that are having trouble staying connected to wireless because they are constantly and endlessly roaming between the 2 closest APs. This causes their connectivity to go up and down forever as when they try to roam over and over they'll drop a few packets and then resume communication. Does anyone have any recommendations on additional items I should be looking into? Here's what I've tried so far:

• No other wireless clients appear to experience this issue. Other clients include Android and iOS devices, along with Win7 and Win10 laptops.
• The SSID in use for the vendor items is separate from their primary (internal) SSID. I have tried connecting other devices to this same SSID and also the vendor devices to another SSID. Behavior remains the same for the tablets, other connected devices have no issue.
• There are 4 APs total. They are Ruckus R510s acting as a cluster where 1 AP is designated the master / controller.
• The 2 closest APs to where these vendor devices will remain have had their transmit power lowered to ~60% to reduce signal overlap, they have had their channel statically assigned (per vendor request in troubleshooting), and 5 GHz has been disabled.
• Load-balancing on the AP / cluster side is not enabled
• Client-isolation is disabled (was disabled for troubleshooting, makes no difference)
• The client did just move to a new building, and 2 of these 4 same APs (with the same settings) were in place at their old location and not really having issues. They were more spaced out and also more obstructed in their old building, so I'm assuming here that that was actually a positive where these tablets are concerned as they may not have attempted to roam due to much further away / weaker signal.

I'm like 99% sure this is an issue of just the base OS for these tablets being a bit old and not handling wireless very well. The vendor has requested that we lock the SSID to only 1 AP closest to the tablets as that is what they recommend. With the way the APs are clustered, this is currently not possible. A full controller would need to be put in place to allow this type of change. I'm trying to avoid that if I reasonably can since these are the only devices that would need that accommodation.

Thanks

edit1: updated some details for clarity