Bailey21 said

My signature is set up as 3 lines. It worked correctly until a recent upgrade and now is strung together on one line with no line breaks.

Please click signature (x): use HTML

then add
after the wordings, which you want line breaks.

for example: David Thomson
XXX company Ltd.
Tel : XXX XXXXXX XX

I think the answer above was trying to indicate the code for line breaks in an HTML signature, but unfortunately the forum software doesn't allow it.

See the picture for the line break code.

@sfhowes

Thank you very much.