Thanks for looking at the site Mike – we have been using browser HTML5 as the player. I’ve tried the Plyr player as well and the issues does seem to persist.
I am wondering if it could be a caching issue – we have the sermon archives and pages set up to be excluded from caching via the Wp-Rocket plugin, however the site host (Flywheel) does use server side varnish caching. According to Flywheel the Wp-Rocket plugin is setup to interface with their caching, but having upgraded from a legacy to cloud hosting account it’s also added a Fastly CDN component.