Invalid argument supplied for foreach() in oembedembedly_providers()

I believe this is a cache related issue of some kind. We're using varnish/memcache...and I'm often seeing this in my logs:

Warning: Invalid argument supplied for foreach() in oembedembedly_providers() (line 43 of /[path_to_site]/sites/all/modules/contrib/oembed/modules/oembedembedly/oembedembedly.module).

When I look at this section, it seems that the providers aren't loaded properly. Clearing the cache allows them to load (once?) and then the error resumes.