Chateau LTE12 passthrough to Ubiquity UDM

Hello All,
I have following setup
LTE12 router with passthrough to UDM.
Everything works fine, problem starts when you perform download 2-3 gigs big file, speed drops to 0.
When replace UDM with another router (USG, Mikrotik or direct pc connection) issue is not observed.
But when connect UDM without passthrough ( double NAT) issue with download not observed.
Ubiquity support didn’t provided any valuable information about that, tried to RMA UDM to the shop, they tested as “normal” router and dont find any issues.
Does any1 have similar setup and faced similar issues?
Thanks in advance.

And also MikroTik on competitor “products”

We not know about that problem.
“passthrough” just give IP to next device and he not change that traffic. More, the Chateau not have internet for his needs - it’s like be offline device.
One customer have that feature and he use ~2-3TB data/mo but he not use UDM - from Ubiquity only UniFi are good and theyrs wifi antennas in my opinion.

You can always try check logs from both devices, grab a WireShark data etc. if you need solve that .
And write to MikroTik support too.

problem was with dhcp, UDM was unable to handle default 1 minute lease time, after support advised to extend time no interruption were observed.