Emails in Fastmail account randomly disappearing from Mail.app
I'm running Mail.app 8.2 (2098) with Yosemite 10.10.3 on a Force Touch MacBook Pro.
Mail.app is randomly disappearing emails from my properly-configured Fastmail account. Emails in my iCloud account show up just fine, but emails to/from Fastmail will randomly not appear in my Inbox.
Disabling and re-enabling the account in Mail.app seems to work sometimes. About one out of three times, the emails will reappear after a disable/re-enable cycle.
I'm pretty sure it's the Yosemite version of Mail.app and not Fastmail because everything shows up just fine in the iOS 8.3 version of Mail.app, the Fastmail web interface and the Fastmail iOS client.
Is anyone else having this issue?
TIA
MacBook Pro (Retina, 13-inch,Early 2015), OS X Yosemite (10.10.3)