Fallout from something that went into production today AFAICT. I've seen it on various desktop Fx mochitest jobs so far.
Transcribed from IRC, Ryan thinks it might be a timing issue, where the retrigger is being executed before the bottom panel has fully loaded, and would be displaying its fa-spin icon.
Easy to repro when using keyboard navigation (left/right) to switch to the next job and quickly hitting 'r' to retrigger ("Unable to send retrigger: undefined"). If you wait a little bit until the data is loaded the retrigger goes fine. Maybe this can schedule a retrigger for whenever the data comes in?
Yup, agreed :) However we handle all th.Notify messages going forward (bug 1148664) the retrigger notifications will be somewhat asynchronous from a UX point of view, so long as everyone is ok with that.
Is this still occurring?
I think this is fixed, I've put in a check in bug 1148864 and we provide a warning (yellow) if the user tries to retrigger a job before it has loaded. I propose we can mark this bug fixed, unless anyone objects?