https://www.phpbb.com/community/viewtopic.php?f=661&t=2547346&p=15469831#p15469831

Inserting bbcode for URL results in extra characters in resulting link. This bbcode;

[url=https://www.citusdata.com/blog/2019/05/30/introducing-pg-auto-failover]this nice[/url]

Results in this URL;

https://www.citusdata.com/blog/2019/05/30/introducing-pg-auto-failover%EF%BB%BF

A little searching suggests that it is exposing the Unicode character U+FEFF is the byte order mark.