Updates from Drupal 9.2.10 to Drupal 9.3.0 are adding an --2 suffix to block-ID's (maybe only views-block-ID's?). For example block-views-block-newsslider-block-1 changes to block-views-block-newsslider-block-1--2, causing all JS an CSS selectors applied to the specific IDs not to work anymore and breaking the design of the website. This happens at least to all block-views-block-Elements of the affected websites.
This happend with different websites and different base themes (Classy, Bootstrap 3).
Setup:
Update from Drupal 9.2.10 to Drupal 9.3.0
Fixed
9.3
Last updated
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Still seeing this on a 10.1 site on a page where a subnavigation is put into one block as well as a Webform into another. The additional ID is only added when loading the second page of the form (which is not configured to use AJAX).
Changing CSS to target the class and not the ID (as advised above) solves it for me, but still this seems like a lurking bug.