Mark,
If all the plugins do the same thing in some scopes, the scopes are at fault. It sounds like they work properly when in other scopes. I do have mine set with the 'level' turned to 'runs after delay time' on the time bases. See if your 10 turn control is at zero and set the contrast control to what you want. Turning the 10 turn pot will make part of the trace brighter as you turn. I assume you have the brightness set to max on the time base to barely see the trace. See if the separation control is set so traces are far enough apart.
Since they work in one 7844, swap the boards behind the working one with another that does not work to see if the problem goes away. If so, it could be a contact problem with the sockets where the sockets are, dirty contacts on the solid state devices that are in sockets on the board or a part such as a resistor is open. The solder on the sockets may be cracked. Resoldering is a PM.
The tunnel diodes you mentioned are the correct ones.
Mark
