something in the federation sender is dropping logcontexts

[richvdh]

Lots of this sort of stuff going on:

2019-05-28 10:32:06,362 - synapse.util.metrics - 111 - WARNING - - Context has unexpectedly changed from 'federation_transaction_transmission_loop-6779' to 'sentinel'. ('_send_new_transaction')
2019-05-28 10:32:06,362 - synapse.util.logcontext - 279 - WARNING - - Expected logging context federation_transaction_transmission_loop-6779 has been lost
2019-05-28 10:32:06,365 - synapse.util.metrics - 111 - WARNING - - Context has unexpectedly changed from 'federation_transaction_transmission_loop-6721' to 'sentinel'. ('outbound_request')

As with all logcontext drops, this is problematic because (a) it means that logs are hard to trace and (b) metrics will be incorrect

[richvdh]

seems to have been introduced by #5037. hopefully fixed in #5277

[richvdh]

fixed by #5277