[size=small][font=arial, sans-serif]Hi, when shooting either a ramp or level time lapse sequence with my Nikon D610 and D600 cameras after a period of time usually about 30 minutes (though this time varies) my camera starts not to fire when the signal is sent from the intervalometer - only firing for every second shot. This only happens when shooting at intervals of less than 10 seconds but I always leave plenty of interval time. For example when shooting a level sequence with a 1 second exposure (everything set to manual including focus)  with an 6 second interval after roughly 30 minutes the camera starts missing a shot and only firing every 12 seconds. [/font][/size]

[size=small][font=arial, sans-serif]I have tried different intervalometers (including the Pixel TC-252 with the LR Timelapse hack) but the problem remains. Any suggestions as to what could be causing this would be much appreciated?[/font][/size]

Does the buffer fill up? (you can see the remaining shots in the shoulder display of the camera). Did you try another SD Card?

The buffer does not appear to fill up (there are lots of remaining shots on display). I have tried different, faster SD cards up to ScanDisk Extreme Pro 95mb/s. This problem only occurs when using a shorter intervals as mentioned above - for example when shooting long 10 hour holy grail shoots ramping to 20 second exposures with a 28 second interval there is no issue.

That's strange. Normally the interval should not matter. It's the dark-time (Interval minus longest exposure) that makes the difference. Normally a dark time of 2 secs is sufficient. Especially if you use the intervalometer with the hacked cable.
You should try to narrow down the reason.

Ok, thank you for the reply Gwegner, I will try to narrow this down.

Ist die Rauschentfernung in der Kamera eingeschaltet? Diese benötigt Zeit und verhindert evtl. Neuaufnahmen - Besser ausschalten!