I checked the metadata content on Gitlab for Riot.im application there links are in <a></a> HTML tag. Seems like this problem happens at the time of translating wiki to application page.
Seems like metadata are submitted by manually through pull request. I was thinking that this is an automated process (fetch data from applications source code repository and arrange it in YML format). Can anyone make a pull request on Fdroiddata repository or only application developers are allowed?