Ardour follow_slave() does nothing (not even seek) if the slave is not locked.
The LTC-slave assumes it's locked if LTC is stable for 5 continuous process-calls.
If the difference of Ardour's transport-position to the LTC-timecode is large (> 2sec), the slave reset itself (assuming drift, seek don't vari-speed).
A LTC-slave does reset does reset the locked counter.
Hence: If initially Ardour's transport differs > 2 sec and the buffersize is small (many process-callbacks), the slave kept resetting itself never informing Ardour that it locked to the external TC, and Ardour never issued a seek.
28c29ab Fix initial sync to LTC with small buffersizes
libs/ardour/ardour/slave.h | 2 +-
libs/ardour/ltc_slave.cc | 13 +++++++------
2 files changed, 8 insertions(+), 7 deletions(-)