No, I do not think that it is possible with the Steem blockchain for an author reward to disappear. If there is a curator reward then there must be an author reward.

It is however possible for the Steemit (and the Musing) interfaces to have hiccups. The best thing to do in this situation (for any post) is:

• To note the author / permilnk.
• To check your the author account (i.e. your account) on steemd.com, the block explorer, to see if the reward is there. Steemd has a better history of the block operations than the wallet on Steemit. 

Or let me know the permlink and I'll check it for you!

The first question I have in reply to yours is, Have you used an alternative site to collect the rewards auto. This can be done on Steemauto and it checks your feed every 15 or 30 minutes to see if any rewards have come in, It will claim any rewards for you automatically.

Failing this the only other way I know that the reward may disappear is if you have got flagged or down-voted on that comment. You can check to see if your reward is claimed or not by looking at your record of your actions on the blockchain.

You can view this record by going to steemd.com/@yourname

https://steemed.com/@francistagbo

You can view anyone's history by changing the name at the end.

I have not experienced not getting a reward myself. I do not keep much track on the reward I should be getting to those I get, Maybe that is something I should keep an eye on for a while just to be sure, 

I have not personally experienced such before and this is the first time i am hearing about it. Sometimes we make multiple post a day and when payout day comes and you want to claim author rewards, Steemit does not differentiate the rewards for each posts instead it presents to you all the unclaimed rewards you have.

So i believe you must have claimed the reward without knowing you did for that particular post.

Funny enough I have heard of it before from another user.

It could be a glitch or an error somewhere. have you checked on Gina to see the history. If it was awarded it would show there.Maybe check steemworld.org as well and double check that it is or isn't there.

Gina should confirm the awards and then you could raise it with musing. Letting them know would be the right option but you need to show them the proof somehow.