Dumpcap issue while splitting files by duration

Hi there, I've an issue with dumpcap command. First of all i'm working in a Linux environment (on Raspbian, on a Raspberry Pi, exactly). I've a PHP frontend, which ask the user to type parameters, and then when he launch the capture (by clicking on a button), the following php code is executed :

shell_exec("sudo nohup dumpcap -P -f \"".$fport."\" -b duration:".$ftime." -i ".$finterface." -w /mnt/hdd/files_to_proceed/REC.pcap > /dev/null &");

My Raspberry Pi is well connected to the network, the capture correctly start and all the packets are captured and stored in correct files. That's a good point. My problem is, if i chose 5min duration for example, dumpcap will correctly split files every 5 minutes, until he magically stops splitting and store all the packets in the same .pcap file during more than 5 minutes. And, about a random time, he suddenly resplit files every 5 minutes correctly. After many tests, i figured out that :
- This issue is independent of the amount of time chosen
- It appears at and for a random time
- Sometimes it doesn't show up and the whole capture is a success
Finally, the tests were fulfill during whole nights (so for many hours), simply because this feature is supposed to work 24 hours a day for several months.

I don't know if you guys already had that issue, if it's due to dumpcap lib or not, but i really need help on this !