WP Version 4.9.8
OSM Plugin Version 4.1.2
Installed plugin, added Widget to the Main Sidebar, set the height to 150, clicked Save. Refreshed the site and map widget doesn’t show.
Changed the default Lat & Long in OSM settings, re-ordered existing Main Sidebar widgets, refreshed homepage and other changes are visible – all except the OSM widget. Checked the HTML markup (Inspect Element) – no trance or evidence of OSM Widget in primary sidebar.
I have 3 other widgets working successfully in this Sidebar.