I've been working on core strength, too! I find a strong core makes a difference with MANY activities. I'm trying to embrace the many Cathe variations of planking...those really help my "stabilizers"! I'll be mindful of engaging my core next time I practice the Crow...I think I need to put a little reminder note on my mat that says "BRACE"!Yoga teachers I've had say it's not about the upper body strength but the core. I find focusing on my core really helps.
Hope you get back to it!