I just tried this with the bold text in your signature without issue, so you'll need to give us more specific reproduction instructions. It may be that it's actually a heading that gets pasted in and remove formatting doesn't remove that (it only removes inline formatting).
Worth also noting that you've mentioned Chrome 70 and unless they're using a different numbering scheme, that's a super old version of Chrome (the current being 83 or maybe 84), so if we still can't reproduce the issue we'd likely ask you to try with the latest version of Chrome. (Chrome support would usually be capped to the current version and at most the previous 2 releases.)