Hi DB,
You will be good in RUT9_R_00.07.01.2 or RUT9_R_00.07.01.4 released today. FW version RUT9_R_00.07.00 contains many major updates.
If cutoff time is consistent then its highly probable that this issue is due a parameter setting. As far as Teltonika concerns there is no default firewall rule that could impact on that traffic. Look at the Logs files to find if any event related to this issue exists.
Try to reduce and increase the timeout parameter, test if that cutoff time periods changes. Switching to TCP is also an option.
Regards
AU