In reality, during my attempts I always used the bright star alignment; I can't suspect any difference in order to have the telescope able to be connected by the INDI driver.
Today I'll try with the other alignment methods, if it works I'll remain curious about why a different alignment method makes the difference: in the end any method only define the sky model used by SynScan to calculate the movements of the telescope to point at a new object, I can't see any reason to deny the connection; that seems to me a pure software choice for which I can't understand the reasons.

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