What kind of messages are you referring to - SMS/MMS or email?
Are you not receiving messages from a particular person, or from everyone? If from a particular individual, is s/he on the same carrier?
What app are you using for these messages?
Sent from my rooted, debloated, deodexed Sinclair ZX-80 running CM -0.001 using Tapatalk 2
Are the people you're not getting messages from in your address book, and do the numbers in the address book exactly (including area code an any prefixes) match the sending number? Check the settings in the message app, and if it's checked, uncheck the blocking option. Also check the spam settings, and see if their messages might be in the spam folder.