Poor signal quality for some channels

Hello everyone.

I am new to the CCM site, thank you for assisting me with a satellite reception issue.

I have a GEANT GN 2500 HD NEW decoder. (decoding via the internet and via cable)
My satellite dish is pointed at ASTRA 19.2 E and connected to the decoder by a single cable.

I have a signal strength of 87% and a quality of 68% for certain channels like ARTE, TV5 MONDE, EURONEWS, M6, W9, F2 which I receive very well, but

I have a signal strength of 87% and a quality that ranges from 00% to a maximum of 14% for TF1, TFX, France 3, FRANCE 4, FRANCE 5, TMC etc., which means that I can’t receive anything. The message displayed is "WEAK SIGNAL."

1) Is it an issue of orientation not being precise enough? How can I make it more precise?
2) Is it a problem with the quality of the connections? Should I change the cable from the dish?
3) Is it a choice of transponder? (It seems to me that you had to choose one once for all!?) If so, which one?

Thank you to those who will take the time to respond to me.