In Microsoft Skype for Business Server 2019 or Skype for Business Server 2015, you define the IgnoreLocal parameter to True in the Set-CsImFilterConfiguration cmdlet to bypass the instant message (IM) filtering on local intranet Uniform Resource Identifiers (URIs) in IMs. However, the IM that contains any URL such as http://contoso.com/site (the contoso.com is the local domain) is still filtered.
This issue occurs because the regex in IM filter isn't correctly parsing the content in HTML or TEXT format. Therefore, the string obtained isn't interpreted as a URL that can't be blocked.
To fix this issue, install one of the following updates: