The same topic was brought up on the 5th of April. It was addressed by Debbie (CM Staff) in the with the following post:
"...depending on how many people you've hidden, the first ones to be added to the list may be removed from the list as you add new ones to the list if you've reached the maximum number of allowable hidden profiles (1,000). I'm happy to look into this further to determine whether or not something might be going wrong, if you send a help ticket with a few examples of people who appear in your hidden list and in your search results/home page."
The thread where the above was mentioned can be found here: www.catholicmatch.com
I was unable to replicate the problem on my computer then - but it does not mean that it was not then, and is nto now still a problem for others. So it seems a help ticket will be the best way to help the staff troubleshoot the problem.