The glue joints between boards can fail, at times, for what appears to be no obvious reason. I have had this happen with both Cascamite and PVA. If it is not low temperatures or old faulty glue, it could be over clamping. Too much force, to try and close up gaps can lead to the glue being pushed out in other parts of the joint.
Rubbed joints of old were often simply that, with hide glue and the boards laid against a pair of battens sloped against a wall - not a clamp in sight.
As for the type of glue for Oak some folk try and avoid using PVA as it can often give a blackened glue line - though I don't find that this happens so much now with the modern PVA glues.