I’ve never used the Recording feature, either FM or Voice on any of my players so I can’t suggest anything but to possibly manually install a previous version of firmware to see if this issue is version-specific. Yes, it’s strange that 1 player works fine, but 3 others do not, even with the same firmware version.
But it would only take a few minutes to test this out, and if you find that the recording feature works fine in a previous firmware version, that would be helpful to the SanDisk dev. team (and ultimately all users) as they could figure out what ‘broke’ the feature in this latest release.