Bold doesn't work anymore, apparently neither does italic.
I have just realized this while answering a question, see screenshot here:
Apparently they don't work on Meta either, while writing this question I have selected bold for the word BOLD and italic for ITALIC and I can't see them in the preview or even after saving.
I am using the same browser as ever (Chrome Version 62.0.3202.89 (Official Build) (64-bit)), nothing has changed, no updates or new plug-ins.