@Stephanie
I've had this problem too Steph - intermittently - with the new messaging system. Most of the time, it's OK, but still very glitchy. Also, even after I've opened a message, it often still shows as unopened. And I responded to a PM Lizzie sent me last week about a mutual friend - took several tries before my message would send, and I'm not sure it even did go through in the end, as I never heard back.
A far bigger problem though is the disappearing messages/big red banner glitch on the forum itself, which has been around for as long as I can remember, and has never been fixed. Regular posters know by now that every message we type out needs to copied before we press the send button, because it's likely to disappear into thin air, but new users wouldn't know that.
There's been a lot of talk on other forums and FB pages from hosts who came here to try and post, particularly since the COVID crisis began (but also long before) who fully believe their posts were being rejected or censored because they kept getting the various red banners when trying to post. It's hard to imagine the numbers of potential members lost to the CC because of this long-term malfunction.