It looks like this is a regression of an old problem? https://community.powerbi.com/t5/Issues/Random-semicolon-in-embedded-report/idi-p/521069 You can see them in some of the Embedded Playground ...
When I use the "Embed a report in a secure portal or website" function I get this issue with the two semicolons on the "Sign-in"-Page (see screenshot). After logging in they disappear. Looks very unprofessional - please fix soon!