Testing by creating new accounts and sending emails to them is not a fully reliable method. New accounts usually deliver messages to the Inbox almost by default, because the spam filters in these accounts are not yet trained. Over time, as these accounts receive more messages, the filters learn and become stricter, and the emails may start being filtered more aggressively.
Regarding our results, we provide specific delivery results based on our seed accounts, and we guarantee with 100% confidence that the emails showing in Spam or Inbox in our tests indeed landed in Spam or Inbox. This is a factual result, independent of any other tools you might be using. You are, of course, free to decide how to act on this information, but if your previous emails were reaching the Inbox and now are showing in Spam, we strongly recommend paying attention to this change.
Your current active users may not be affected, as inbox providers generally prioritize emails to engaged recipients. However, new recipients are more likely to see your messages in Spam if this situation continues. Additionally, you may look at the result returned by the Google Spam Filter or the Microsoft Online Protection filter, which is an independent signal beyond our testing. It would be wise to monitor this situation to avoid potential delivery issues in the near future.