I'm getting a warning that my Sonar membership will go into Demo mode in 13 days, and says to renew my membership or buy Sonar before time runs out.  So is it not a recurring membership like I thought it was?

Are you paying monthly? If so you need to complete 12 consecutive payments before you own the software.
If you buy an annual membership it will not time out since you own it outright.

Well yes, I'm paying monthly or I wouldn't be concerned about a warning to pay or lose. :-)
 
Any other monthly subscription or membership that I've ever had with other companies, have never threatened me, they simply take my money each month as expected.  Why does Cakewalk bother their users with a warning that's not warranted?
 
By the way, not long after starting this thread, I received email notification of my membership being renewed for another month, so apparently the payment IS automatic.  But that warning certainly made me nervous.

Hi, the fact that you get this message is because your membership has actually lapsed and that you are now in a grace period. This is most likely because of a billing issue with your CC or you didn't pay for the next month. This is a very common way to let you know that if you don't renew by the end of the grace period it will deactivate. If everything had gone through smoothly with the billing you would not have got that message. If you think you shouldn't have gotten this contact support.
 
If we didn't have this message you would launch SONAR at the end of the grace period and be permanently in demo mode. That gives you no time to react and do something...

I first ordered Sonar on January 27th, and according to the order confirmation the next payment was due February 28th.  I got the warning one day BEFORE the payment was due.  So how could my membership have lapsed? My credit card is in perfect shape, so there couldn't have been a problem.

I would contact Cleverbridge to see if there's a payment issue. That doesn't sound right. In looking at your account, it seems to be ok. Can you restart Command Center too and see if that fixes it?

Interestingly, last night I did start Command Center, and not long after that an automatic payment was processed. But I'm not sure how that could be related, since I've run Command Center a few times since my initial purchase, for updates and such.

Mine frequently says it's in Demo mode for about 2 minutes after I start it, regardless of when I last ran Command Center (in fact, I'd just updated yesterday, and it did it again today) and then suddenly it pops up with a message telling me everything's ok.