Given you got the correct USS message from the client PCOMM, this means the connectivity to z/OS through Linux was good. Since you got this far, you should have gotten a TSO message on the z/OS system console when you tried to log on and failed. Could you see if you got messages after attempting to log on to TSO? They will help tell us what is wrong.
Also, the following information will help.
1) The 3270 definitions in your devmap. They should look something like this:
name aws3274 00xx
device 0700 3279 3274 mstcon
device 0701 3279 3274 tso1
device 0702 3279 3274 tso2
2) It would be nice to see the LU definitions in the local non-SNA major node that match the channel unit addresses in the devmap, The local non-SNA LU definitions give the terminal type, and must be correct based on the terminal trying to connect. When the logon screen comes up, you typically see the local non-SNA LU name. I can see what looks like MVEX03 on the pcomm logon screen. Can you issue a D NET,ID=MVEX03,E on the z/OS console after starting the PCOMM session? Also, when you bring up the logon screen for the X3270 session on linux, it should also have a local non-SNA LU name, probably something similar to MVEXxx. If you could issue a D NET,ID=xxxx,E for that LU name, that would help see which one got used that works.
3) Finally, when you display the D NET,ID=xxxx for the x3270 logon screen LU name, the one that works, at the bottom of that display will be the TSO appl name that is in use. Something like this:
NAME STATUS SID SEND RECEIVE
A06TSO01 ACTIVE-P xxxxxxx 0005 000E
Could you do a display of that name - D NET,ID=A06TSO01 (or whatever its name is). That will help us know which TSO major node is being used.
RDTBebe