What a pain in the ash. If it's just the glue joint and not the ash splitting, then I think the answer is easier to figure out.
Is it humid where you are? Here in MN, our humidity wave doesn't really kick in until about the end of May. Then it is thick like Florida for a few months here. Nearly every MN home has a moldy basement from our swampnuts humidity every summer.
When gluing in high humidity, I would just allow more time for the glue to dry. As Stv said, waiting a full 24 hours, at least, never hurt any project. If you already waited 24 hours and the split still happened, I would personally start thinking I got a bunk glue bottle. The Ramones would not be happy.
I don't think it's a clamping issue personally. Once that glue dries, that split would never happen IMO. Glue joints are strong AF when it comes to wood. As long as the glue bonds with the wood, it's set in stone once dried. Glue never has a problem bonding with ash, it's not oily AF like bocote.