Messages were slow to send. Uninstalled / re-installed latest available v1.5.0 DMG. Now will not connect at all.

Same here
as mentioned in the other issue:
macOS High Sierrra 10.13.4
/Applications/YakYak.app/Contents/Resources/app/node_modules/hangupsjs/lib/init.js
html = html.replace(/?script>/gm, '');
to
html = html.replace(/?script.*?>/gm, '');
Actually that is a syntax error (from the extra /). This worked for me:
html = html.replace(/<\/?script.*?>/gm, '');
Most helpful comment
Actually that is a syntax error (from the extra
/). This worked for me: