OK I got the answer from forum user "Fred Pluebell":
"A likely explanation: The same TDPID, but with more COPs, is defined to point to a different Teradata system (in your hosts file or nameserver/DNS). That's easy enough to check: "ping TDPIDcop2" (or one number higher than the highest "cop" you defined).
CLIv2 will enumerate and attempt to resolve the "cop" suffix names in sequence until it gets a failure, then randomly pick one from the list to use as the starting point. If "cop1" points to system A but cop2 through copN point to system B, that could explain the behavior you observe. "