Megabyte-
You may have had Aloha's patch installed on your 98 machines, been running Netbeui or a host of other variables that may things go smoothly. I didn't mean to suggest they won't work together, they will- I just meant reading this one issue. But will see this problem 100% of the time if it isn't addressed and your using TCP/IP.
I had the unfortunate experience of having to resolve this one myself and it was a huge headache. In a nutshell, after 10 or 15 minutes of being up and running, some or all of the Win98 boxes will start to "blink" on and off from a floating logo to "Cannot locate Master" or whatever, usually back and forth to where the terminal is pretty useless. And usually the master itself if I recall correctly, would be fine. (pardon my lack of precise information, I think I tried to remove this one from my brain due to trauma).
It would almost look like a permission issue or master browsing issue. So after spending a few hours (quite a few)
trying to figure out what it was, I decided to put the server's IP as the default gateway and it stopping now and forever.
I don't know all the specifics- maybe if your XP file server and master terminal was XP too, with other machines being 98, you wouldn't see the issue. I never tested it that thoroughly. Years later, I found out Ibertech had a patch for 98 boxes, but I never used it. But sometimes when I upgrade and older machine to XP, this issue will still bite me in the azz for forgetting to put in that default gateway.
They 4695's were ok, they started to have weird touch screen issues after like 4 years I wanna say. But honestly, I really don't think you should expect all your terminals to last that long... 4-5 years isn't great, but it's not terrible. I thought the SurePOS 500 was ok, I still have a location that still has a few kickin and it's been close to 9 or 10 years? My only real issue with them is that they had a numerous revisions in a short amount of time, so you could have two or three in one location that had vastly different hardware configurations (some with actual serial ports, some that ran serial from an ethernet connection- different touch drivers, etc). Just enough to make imaging a pain in the butt.