Hi @maans ,
Please check if there is overlay for the /libs/cq/xssprotection/config.xml for the same in /apps and there is change in the configuration for the a tag as shown below (default config)
If html tags are getting lost in RTE are mainly due to AntiSamy rules in AEM. Please check the error logs for the same(org.apache.sling.xss.impl.HtmlToHtmlContentContext AntiSamy warning). If not, then please add your error logs.