Are you using a NULL modem cable? They don’t work with Gen6 nodes.
simple 3-wire null modem cable that doesn’t support hardware flow control:
No hardware handshaking
The simplest type of serial cable has no hardware handshaking. This cable has only the data and signal ground wires connected. All of the other pins have no connection. With this type of cable flow control has to be implemented in the software. The use of this cable is restricted to data-traffic only on its cross-connected Rx and Tx lines. This cable can also be used in devices that do not need or make use of modem control signals.
Hardware flow control was listed in the requirements for gen5 and earlier too, but somehow that cable was working with those nodes.
This cable is incompatible with the previous types of cables’ hardware flow control, due to a crossing of its RTS/CTS pins. With suitable software, the cable is capable of much higher speeds than its predecessors. It also supports software flow control.
This is the one that works: