Bounty failed despite succeeding.
To get an official answer, you’d have to create a support ticket and work with customer service. What follows is my impression.
There are two timers you have to beat:
- The event timer on defeating Tessa.
- The overall timer for the bounty.
The screenshot you showed doesn’t indicate whether you succeeded in beating either of those. I have seen more than a few guilds fail one or the other of above, and (some) members were convinced (at the time) that the bounty was defeated soon enough for both. The individuals in question only were able to change their mind, because other folks had been watching the timers and/or actually had screenshots.
In this case, the screenshot shows Teesa yielding at 5:03, the bounty failing @ approximately 5:03 (one minute before 5:04) and being started at 4:48 (16 min before 5:04). That’s consistent with barely missing the deadline for the training.
That doesn’t mean you didn’t encounter some sort of bug; it just means that there are other possible explanations.