it seems that the built-in Link Validation scheduled job has been failing for one of our customers for quite some time because there are some links with "tel:" scheme. Such links should be ignored by link validation. Same probably goes with "mailto:" links. Peaked at the code and currently it is just checking if link is http or https, if not, throwing exception and seems the execution is totally stopped so no other links are checked.
You can ignore such links by using the `excludePatterns`, or my preferred solution: