K3 could be just fine.

With power off, the relays are in their receive position as shown the the schematic.
The antenna is grounded for your DC ohmmeter by way of T2, via L4,3,2,1, K1 and K2

As per my previous post, my guess is that when you power up it immediately goes into transmit mode.
Now the antenna is grounded by way of T11, via KA1,2,3, L11,12,13 and K3.
In either case, all of TP1, TP2, TP8 and the antenna are DC grounded.
That would be true of a perfectly functioning rig, except it should not power up in transmit mode.

I'm guessing a miswire or two in following the hfsignals ubitx wireup instructions.
Perhaps in that 4.7k resistor that should be on the morse key line.
And perhaps also somehow in how the mike got wired up, such that plugging in the mike
somehow brings it back to receive.