"An unexpected error occurred." during changing of workflow status for issue (BB-10435)

Repo: https://bitbucket.org/iit-cem-team/com-event-man

When developer tries to change the workflow status for any issue from "NEW" to "OPEN" the error message "An unexpected error occurred" is shown in the status popup. Please see attachments.

Not all developers of mentioned repository have such problems.
We know that problem reproduced for the following developers: vadim_mihalovski, Nikolay_Kvetko.

The following https://bitbucket.org/iit-cem-team/com-event-man/issue/3/confostisnet issue can be used to reproduce the error.

We also find similar issues created by other developers for bitbucket issue tracker: https://bitbucket.org/site/master/issue/7740/workflow-resolve-fix-issue,\\
https://bitbucket.org/site/master/issue/8857/issue-tracker-not-fully-functional-an\\
but no solution are provided for them.