The 1.37.0-wmf.12 train is currently blocked at group1 by an UBN bug:
The culprit seems to be  which added strict type checking to some methods that are being called in a disagreeable manner from LUA code. For the short time that wmf.16 was deployed to all wikis, errors were occurring on at least svwiki and yuewiki at a rate of 900+ fatals per minute.
A clean revert of the offending patch isn't possible because other code built on top of it. For now at least it would appear that the train is blocked. Any assistance with resolving the issue is appreciated as always.
To keep up with the most current status please watch the train blocker task in Phabricator.
- 💕- Your humble train conductor.