MTU issue to server with tow NICs

Dear Networkers, I have strange problem. Our server Team has a VM on Hyper V with to NICs each in separate subnet. One NIC has a gateway and one only route to 192.168.0.0/16 subnet. Problem is that there is a problem with working on this device (linux) listing a larger amoun of data breaks the connection or the connection hangs somwhere. When changing MTU to 1400 everything seems to be normal. I did some pings with size 1500 and everything seems to be fine. Our offices are connected with MPLS from provider, one lst office without MPLS seems to be working correctly. What am I missing here? only thse servers with two NICs has a problems. Thank you for any provided help