Hello, after upgrading to debian buster with kernel 4.19 we also had problems.
By adjusting net.ipv6.route.max_size we have fixed the following messages: watchdog: BUG: soft lockup - CPU#X stuck for 22s! and ixgbe 0000:02:00.0 ens2fX: initiating reset due to tx timeout But we still had a lot of jitter on the line. Downgrading to 4.9.0 fixed the problem, but this is not a permanent solution. What else did we tried: * Increasing gc_threshX net.ipv6.neigh.default.gc_thresh1 = 2048 net.ipv6.neigh.default.gc_thresh2 = 4096 net.ipv6.neigh.default.gc_thresh3 = 8192 => Did not help * Going to a backports kernel (5.7.0) => Did not help @Frederik Kriewitz: What did you do fix that problem? Oliver