In your bug 1400568 you wrote "This is recent bug, as of 52.3.0, never happened before". So in that bug (which is duped to this one), and here, we have proceeded on the assumption it's a regression - regardless of whether it's a race condition or not. Looking back, there is also bug 1422251 and bug 1440716. So you are not the only person to have reported this issue against version 52. Still, it was only 3-4 people to report the issue for all or most of version 52. So changed in newer versions make the situation worse. But certainly it's possible part of the underlying issue predates any of these bug reports, and the regression hunt is a waste.
Bug 1381485 Comment 261 Edit History
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In your bug 1400568 you wrote "This is recent bug, as of 52.3.0, never happened before". So in that bug (which is duped to this one), and here, we have proceeded on the assumption it's a regression - regardless of whether it's a race condition or not. Looking back, there is also bug 1422251 and bug 1440716. So you are not the only person to have reported this issue against version 52. Still, it was only 3-4 people to report the issue for all or most of version 52. So change(s) in newer versions make the situation worse. But certainly it's possible part of the underlying issue predates any of these bug reports, and the regression hunt is a waste.