Reduce the tcp-initial-timeout default
This is currently set to 30 seconds. Discussions in the BIND team meeting on 12 March 2019 tended towards a consensus that this was too high and should be reduced.
ARM description:
tcp-initial-timeout
This sets the amount of time (in units of 100 milliseconds) that the server waits on a new TCP connection for the first message from the client. The default is 300 (30 seconds), the minimum is 25 (2.5 seconds), and the maximum is 1200 (two minutes). Values above the maximum or below the minimum are adjusted with a logged warning. (Note: this value must be greater than the expected round-trip delay time; otherwise, no client will ever have enough time to submit a message.) This value can be updated at runtime by using rndc tcp-timeouts.