If I put a midi sequence into a loop it keeps time for about 3 iterations then starts going out of sync, at the moment I can overcome the problem by freezing the sound module, ie making an audio file and playing from there. But this can get irritating when I want to make minor adjustments to the midi. This is not the norm as I have experienced in previous versions. HELP!

Make sure you loop is an EXACT number of measures before invoking it as a loop.
 
Also make sure your loop points are in the exact spot they should be.

theword
If I put a midi sequence into a loop it keeps time for about 3 iterations then starts going out of sync, at the moment I can overcome the problem by freezing the sound module, ie making an audio file and playing from there. But this can get irritating when I want to make minor adjustments to the midi. This is not the norm as I have experienced in previous versions. HELP!

How are you looping? For MIDI you need to create a groove clip. A grove clip has rounded corners to distinguish it from a normal MIDI clip.