Similar issue driving me crazy. My phone (18.2b3) is fine. my ipad mini (18.2b3) syncs up with the phone perfectly. My m1 macbook pro (Sequoia 15.2b3) keeps missing messages. I thought it was mostly in a group chat with android users, but it just happened now with a collegue who is on an iphone too. she texted me, it showed up on my phone, my ipad but NOT on my laptop. Other texts do come thru. I've logged out and back in of icloud messages, manually picked sync imessage in cloud in the app and in the settings. Rebooted more than once. And it still won't download a bunch of texts that came thru on the other devices. Has gaps here and there. Frustrating.