When an external URL is parsed by Drupal, notably when one is entered into a Link field, any array query parameters that do not have keys will be rendered with array keys added. Drupal\Component\Utility::parse() uses parse_str() to convert the query string into $options['query'] and that's when it happens.
https://example.com/?f%5Bcollection_name_ssi%5D%5B%5D=Examplehref=""Field will render with href="https://example.com/?f%5Bcollection_name_ssi%5D%5B%5D=Example"
Field renders with an extra 0 in the href:
https://example.com/?f%5Bcollection_name_ssi%5D%5B0%5D=Example
Edit the node, and the 0 is not in the URL field. Render the node, and the 0 appears in the markup.
Active
11.0 🔥
base system
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
#11 shows that the parsing is performed by the base system, not the Link module.
For the record, I've run into this problem too. There's a third-party system used at work that has un-keyed query parameters. I had to tell our content editors "You can't link to it from Drupal because its URLs are incompatible with how Drupal parses them" and they had to develop workarounds for the problem like using tiny URL services.