Mail has no content

I can read the content of all emails on my Mac mini (macOS 15.6.1) and iPhone (iOS18.6.2), but not on my Mac Air (macOS 14.8.1). This also happens when I'm home and all 3 devices are linked into the same WiFi source. On the Mac Air, for 1 in 5 emails I get the top of line information, but not the contens. Quite frustrating. Any suggestions? Thank you in advance.