I recently enabled “Automatically schedule recommended WOTD.” I have Mondays blocked off as unavailable, but yesterday, the planner decided I should do a 40 minute ride anyway. 
Hey Jim,
I’m guessing you have the auto-schedule a recommended workout option. With that enabled, Xert will always pick something, even if you have a scheduled rest day, just in case you still wish to hop on the bike and do something on your rest day! 
Most often, it’ll be a relatively short & easy ‘Active Recovery’ workout selected on a rest day.
I’m glad to see that the red “failure” indicator goes away eventually. 
Hmm…Today, I’m supposed to do 99 XSS of low intensity training, but XSS buckets on my Edge 530 seems convinced that I should be doing the 27 XSS optional workout that XFAI suggested for my rest day yesterday, even though that workout has already been removed from my calendar.