For anyone stumbling across this in the future still looking for an answer, a support rep replied to my ticket and suggested this is a known issue with SP17 on 6.5. Ref: CQ-4353652 Good luck all!

Setting the log level to debug does not appear to generate any additional log output information. Wondering if I'm missing something in the configuration there... but otherwise nothing sticks out? Same error as in the original post is present, nothing more. As for SMTP access

Not on AEMaaCS, this is AMS/ACM. Regardless, going to see about accessing to grab the error.log.

Will see about grabbing the full error.log. ...validate : That the AEM instance can successfully connect to the configured SMTP server. Yes, this instance is able to access the smtp server.Confirm that the submitting user and assigned group have valid email addresses associated with their user accou...

The old tried and true. This was the first thing we tried though!

Well, that's the thing... This is all that is being posted in the log. 

Hello all! The community has been very helpful with past issues, so I figured I'd bring this one here as well - Perhaps you'll all have some ideas. I've seen a lot of people with EMailNotificationService or various other workflow-email-related issues that are typically configuration errors resolved ...

Seeing the same issue across both development and stage on our AEM 6.5.12.0 instances, while working in Touch UI over this last week: "The issue is that periodically ALL components will have their edit options removed, just leaving the Insert and Group options."   Moving my reply to a new post for v...