Core Sleep

Do you feel fatigued, or have other problems in your daily life that seem to point to poor sleep quality?

I'm assuming you're getting the "less core sleep" info from some kind of fitness tracker or similar. Having had the opportunity to compare my tracker's result with the same night's in-hospital sleep study at one point (when I was wired up for every biometric thing a person could think of), I don't take my tracker's sleep analysis very seriously at all.

If you perceive sleep quality issues affecting your day, that's a different matter.

If that's the issue, start with things like sleep hygiene (web search will give you many ideas), maybe log your sleep and your subjective feelings next day for a while, see if you notice any patterns with respect to workout timing, caffeine, eating times, etc.

"Core sleep" is not one of the standard sleep cycle terms I'm familiar with from my reading, so I can't really say anything specific, and I'm not an expert anyway, just someone who knows a bit from having her own sleep issues.