FPS goes from 50 FPS to 25 when imported

Yes, this is common and most likely when you playback that footage its played at 25fps but since its shot on 50fps your footage will seem to be running at 50% speed. You can right-click and look for Interpret (its in a submenu) and change 25fps to 50fps. This changes the frame rate of the playback from 25 to 50, meaning from 50% to 100%.   This is usefull in many other cases. If you have real film grain assets that are capture at 24fps and your sequence is 25, when you edit that grain into your timeline, under the hood, it will get time-stretched from 24 to 25 meaning there will be some frame blending. If you go to interpret and change 24 to 25 then the grain will be running at 25fps as if the film projector was running at 25fps and capture on video at 25fps. This might not be visible for 24 to 25 projects but might be visible in 24 to 30fps projects. Hope ive helped.

Nomenclature matters.

When talking about video specs, you always and only list out the frame rate.  Many cameras get this wrong, however, and list the field rate.  For example, 50i.  Technically, that means 50 interlaced frames per second, and there just is no such thing.  It should be listed as 25i, which means 25 interlaced frames per second.

My guess is your camera is listing it wrong.  Most do.