Why are you monitoring the neutral? This will only give you the out-of balance current, which although your energy supplier would like you to reduce to a minimum (ideally zero) so that their out-of-balance demand is minimised, is largely meaningless.
I can’t think of a good reason why your emonTx4 won’t communicate with the new emonBase. When the emonTx4 was introduced, it was decided to change the library (and hence the format of the radio message) from JeeLib to LowPowerLab. Unless you mentioned your existing emonTx and emonPi when you bought the new units, they will be using the LowPowerLab library and a different radio format to the existing.
They should work, unless you’ve updated the emonBase and the emonTx4 to different formats – one to RFM69 LowPowerLabs and the other to RFM69 JeeLib Classic.
This also explains why the emonBase can’t see your old emonTx3.
One thing to note, although the message formats are different, both use the same radio channel, so you can expect “collisions” occasionally that will mean both systems lose the occasional message, even if you update everything to use a common message format.
Jeff’s post is Can’t get the Serial Config Tool to work with computer equipped with USB-C