Exported Video not running at normal speed. Audio out of place synced.

Hi can anyone help me, please?
Since i’ve updated Adobe i’m unable to export the exact timeline into a video.
When i play it back the audio’s unsynced. Clips are missing and not running at the speed i had in the timeline.
Even when i use media encoder to proxy a file using the standard ‘match source medium bitrate’ the proxy video is exported at 30fps? The original was 50!
Can someone help, please? i’ve spent a lot of time on this latest video.
Thank you
Andy