[wp-trac] [WordPress Trac] #54907: After upgrading to 5.9 I get blank screens when trying to edit or add posts

[WordPress Trac]

#54907: After upgrading to 5.9 I get blank screens when trying to edit or add posts
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 Reporter:  eTurboNews    |       Owner:  (none)
     Type:  defect (bug)  |      Status:  new
 Priority:  normal        |   Milestone:  Awaiting Review
Component:  Editor        |     Version:  5.9
 Severity:  normal        |  Resolution:
 Keywords:                |     Focuses:
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Comment (by ldigregorio):

 Good news...found the reason for the error message: "The error in both is
 "Publishing failed. The response is not a valid JSON response." ---it's a
 security issue. Got past this. Was unrelated to core5.9, but the first one
 (white screen when trying to access beta editor in single site with no
 plugins but one (classic widget) I think probably is related.

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Ticket URL: <https://core.trac.wordpress.org/ticket/54907#comment:11>
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