Demodulating a satellite BPSK signal
It is difficult to advise about the noisy constellation.
If it is a channel with no added noise, the constellation looks bad.
Not easy to investigate but here are some suggestions to explore:

The signal power might be too low, too close to receiver sensitivity level, so the noise you see on the constellation could be the one of the receiver.
Try to increase the power of the signal to be out of the receiver noise zone.

Automatic gain control issue: Try to freeze the power and AGC or bypass it if possible check the result

Synchronization recovery issue: Synchronize the transceiver and the receiver with their 10 MHz (so you have no carrier and sample offset). Then you can bypass symbol sync module in GNU radio

RCC filter: Maybe your filters do not have the same response in the transceiver and receiver. You could check their roll-off