As a frequent commenter-from-review-queues, I've notice a high frequency of errors in doing so in this past week. This is a definite change in site behavior. The error is frequent but not deterministic.
For example, I tried to add my Comment on this Close Vote review item, and it failed with the red background pop-up message "An error occcurred...". I then drilled down to the underlying Question thread and successfully posted my Comment there (cut-and-paste from the initial attempt).
Note that this item was not a Review Audit, for which some queues seem to have had the Commenting function disabled in a fashion. I suspect that a recent tweaking of this disabling implementation (to better disguise when review items are audits) may have had this undesirable (error prone) side-effect.
Related from Meta.SE
One of the Answers there seems to discover that this intentionally occurs for some Review Audits, but I've been aware of that for some time. The Meta Question itself is pointing out the Edit Comment function from Review Queues is impaired similarly.
Update (4/22/16): I've now gone several days without the errors in posting Comments from review queues (except one or two audit cases). Very likely there was some fix in the system software. If I can get some confirmation or details about the hypothesized fix, I'll post that as an Answer.