I think the problem arises from moving the plugin settings from [Settings] in the .ini file to [Settings/UKTides_pi].
On the Mac I removed the opencpn.ini
file and the opencpn/plugins/UKTides_pi/data
Restarted OpenCPN. One warning about the previous crash and then everything worked correctly(?).
This is a bit dramatic. Suggest editing the .ini file. Remove any references
to UKTides and save. Restart OpenCPN. Test the UKTides plugin. The settings (these include the dialog position) will be saved in [Settings/UKTides_pi] on closing OpenCPN.