Gents,
i had dropouts during the playback of a large project 
(71 tracks (ca 30 frozen), 6 synths (4 frozen)and several fx.
It´s only the kick of ad drums which had random dropouts while using a buffer of 1024 samples.
The dropouts disappear when I change the buffersize to 512 samples or lower.
 
I´m recording  in 24 bit and 44,1 khz.
 
Does anybody have an idea why this happens ?
 
 
 
 
 

Raise the 'Prepare Using' Buffer in Preferences > MIDI > Playback and Recording to 500ms if it's at the lower default of 250ms. If it's already at 500, you can try increasing in increments of 100ms until the problem goes away.

Thanks a lot for your hind.
The midi buffer has been  250 ms , so I will try 500 ms 
tomorrow .
 

Pragi
Thanks a lot for your hind.
The midi buffer has been  250 samples , so I will try 500 samples 
tomorrow .
 

It's not samples, it's milliseconds

@ brundlefly
Done,
setting the midi buffer to 500 ms
and the audiobuffer to 1024 during the mixing session works.
Thanks
 
@Bob ,  the measure (ms instead of samples) is corrected.