I experience strange behaviour ever since i upgraded from 18.06.1 to 18.06.2 on an D-Link DIR-860L. I have 4 of these devices on 4 different PPPoE connections running. 3 of 4 devices are updated to the latest stable build, and exactly these 3 devices are having the same replicable problem: For the clients behind NAT (i only use IPv4 on WAN and LAN side) the internet connection randomly drops for less than 1 minute until it is working again - this happens about 1-3 times an hour. Since this also happens to wired machines, it shouldn't be a WiFi problem. The connection time of each interface does also not reset when this occurs. Since i am using builtin DNS and also external DNS (OpenWRT/ M$ AD / Pihole) on different Networks, a DNS-Issue should be also out of scope. I am using local IP ranges within 10.100.10x.xxx. I haven't noticed any problems from LAN-to-LAN connections so far. In addition, i don't find anything strange in dmesg or kernel log, but that's just my opinion. I believe there's some sort of packet loss, but i don't know where to start looking for the problem. Maybe somebody can help me to narrow the circle if it is misconfiguration or a bug. It was working flawless when using 18.06.1.
Have you enabled software and/or hardware flow offloading?
Not that i am aware of. I've read about this the very first time and haven't encountered such optimization features until now.