I had the same problem using newer versions of Cura with a MP Select Mini v1. It looks like it's because the printer gives an unusual response to the temperature command that Olvin mentioned. In the case of the Mini v1, it responds with something like:
b'ok N0 P15 B14 T:45.9 /0.0 B:26.4 /0.0 T0:45.9 /0.0 @:0 B@:0\n'
I have no idea what those "N0 P15 B14" values mean, or if the Mini is wrong to send them, but the USBPrinting plugin doesn't like it. In one spot it only accepts "ok T:":
And in another, it expects either a line containing "ok " followed by "B:" or "T:", or a line starting with "B:" or "T:":
I don't have a Mini Pro to test with, but I wouldn't be surprised if it's also confusing the plugin by responding with something similar. As a quick hack, I can make it work again by changing the:
if b"ok T:" in line
in both those places to just:
if b"T:" in line