Hi,
I would ask a clarify about Frame Angle check in Align tab.
If i have a previous frame with a specific angle, like -0.50° and I use it for build a sequence in Ekos, it load this frame and compare it with the current frame captured.

If the captured frame have an angle of 179.50° it is rotated of 180°, but it is specular and Ekos advice me to rotate the camera to reach the original angle of -0.50
Could thi notice to be ignored??? if the current angle is plus o minus 180 i think that this notification could be not necessary.
During last session I lost abount 40minutes after meridian flip because Ekos requested me to rotate the camera, but the angle was rotated of 180°

During last session I lost abount 40minutes after meridian flip because Ekos requested me to rotate the camera, but the angle was rotated of 180°

I suppose you are using "Manual Rotator", aren't you? Since KStars 3.5.7 you can set *Flip Policy" to "Preserver Rotator Angle" in the align options. This option prioritizes the present rotator angle after a flip and thereby EKOS accepts a rotation of the camera position angle by 180°. Just assure yourself, that "Threshold" is big enough to fulfill the limit of 30 arcmin, if you want a range of 0.5°! (Default is 10 arcmin!)
BTW: How did you lose so much time? Wasn't it possible to cancel the rotation request window of "Manual Rotator"?

Yes I does not have a rotator, if the original frame have an angle of -0.48° at the start of the session i can set the angle again to -0.48 (or near it) or at 179.6, in that case the imge is fplipped but angle is respected.

I lost 40minutes because Ekos was waitin for a decision, but i do not stay all the time looking at the stuff during a session

I looked at the Flip policy and it is setted as Preserver Rotator Angle with a Threshold of 30, but Ekos tell me to rotate the camera to reach the original angle of -0.48.
I disabled the rotation check after the first alignment

Hi Alessandro
I just ran a test with an image taken on pierside west with a camera PA of -0.01°. A "Load and Slew" of this reference image slew the mount with a flip to pierside east and ended without requesting an interaction from "Manual Rotator".The camera PA was then 179.70° and the "Manual Rotator" reported "Current PA is 179.704; Target PA is 179.995; diff: -0.290695" ("Flip Policy" was "Preserve rotator angle" and "Threshold" 30arcmin.)

So the question is: Does your reference image have pierside information? If not, the process cannot succeed!