I've had leaks develop from the pipe joints on my 2" main PVC lines that feed solar network for pool heating. Tech pages say pipe should be painted white but will that do anything for the couplers? That's where the problems are occurring, so I imagine it must be something to do with the glue bond breaking down. System is tens years old...thanks for pondering this out there!
PVC (plumbing) is not rated for sunlight exposure and needs to be painted or otherwise shielded from sunlight.
PVC (electrical) is not rated for plumbing/pressure use, but is UV resistant.
So, if you have unprotected PVC pipe in the sun, expect more problems. And paint it, though already-damaged sections may still fail after painting due to existing damage. Paint should be applied after assembly, including couplers/joints.