Since you got both test messages… it’s probably not a spam issue.
And since it (notifications) started working again - I’m guessing perhaps it’s WebFlow.
- but am not 100% sure. Contact them.
What we need to figure out / the more important issue… (if it’s WebFlow)
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- is the message / notification being delay (ie: you will eventually get it)
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- or is gone (ie: WebFlow server killed the message and will never deliver it).
If it’s “1”… hopefully the delays will not be long.
If it’s “2”… only way to test this is to constantly send test messages from your site and see if you receive them (boooooo) 
This would be something for WebFlow to answer.