[wp-trac] [WordPress Trac] #54230: Block based widgeteditor can't update "Not a valid JSON response"

[WordPress Trac]

#54230: Block based widgeteditor can't update "Not a valid JSON response"
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 Reporter:  davidlarssonback   |       Owner:  (none)
     Type:  defect (bug)       |      Status:  new
 Priority:  normal             |   Milestone:  Awaiting Review
Component:  Widgets            |     Version:  5.8.1
 Severity:  normal             |  Resolution:
 Keywords:  reporter-feedback  |     Focuses:
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Comment (by joegasper):

 Same issue, just Widget editor fails. Tried everything you'll find on this
 error. Running IIS, don't have a site that it works, single or multisite.
 This is a screen recording of a generic site, 2021 theme. PHP 7.4 - no
 errors. MySQL 5.7.25.
 https://1drv.ms/v/s!AhHWmqEUaqs0hI0S7RPk4757r8ud7w?e=enfgpn

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Ticket URL: <https://core.trac.wordpress.org/ticket/54230#comment:5>
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