Concerns About Declining Email Deliverability Scores Before Cold Outreach

Hi folks, I have a general question about cold outreach—hope this community is the right one to ask and that it can help me out. I have several inboxes that I’ve been warming up for months, but I haven’t sent any cold emails from them. My deliverability score has been at least 98% for all of them, and most of the time it was 100%. However, I noticed a few weeks ago that the score started to drop, and now some inboxes are even at 94%. I haven’t changed anything or started using them for cold outreach, yet the score is decreasing. Any ideas why this is happening and how to fix it? Thanks in advance!