I've been having the same problem and I just discovered that if I hold down the center scroll button on my mouse it has the same function as holding down the spacebar. This doesn't answer the question as to why spacebar no longer activates the pan tool but if you are using a mouse it is a good alternative.
Temporary switch to pan tool with spacebar not working correctly
in Troubleshooting
Posted
I've been having the same problem and I just discovered that if I hold down the center scroll button on my mouse it has the same function as holding down the spacebar. This doesn't answer the question as to why spacebar no longer activates the pan tool but if you are using a mouse it is a good alternative.