[caoilte]

When I switched family on Xmas day 2019 it took hours for contact data to sync so that it was possible to message each other. WhatsApp setup took seconds to propagate. Luckily I was eventually able to persuade it was worth waiting for signal.

[MayeulC]

I saw someone with this issue on HN the other day. Though I've never had that myself, you can apparently pull down to refresh the contact list within Signal after tapping the "write new message" (white pen on blue background) icon.