i staerted to post this a couple of days ago - there have been a number of posts since then so might be redundant, i have had this issue, intermittently, over a number of releases, going back a couple of years at least i would say. Often it clears by a refresh for the folder or a TB restart. Sometimes its a specific email as well as a whole subfolder of emails.
Bug 1890230 Comment 89 Edit History
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i staerted to post this a couple of days ago - there have been a number of posts since then so might be redundant, i have had this issue, intermittently, over a number of releases, going back a couple of years at least i would say. Often it clears by a refresh for the folder or a TB restart. Sometimes its a specific email as well as a whole subfolder of emails. In addition i now have compaction to run on approval not Auto, no filters and all my accounts are IMAP