The 115 is a different model from the 215 and requires different firmware (Pegasus vs. Centaurus). If it is a GA release of code, if the VC differs in model from an IAP that is trying to join, it requests the image server for the GA version of code for that new platform.
A certificate on IAPs with versions older than 4.1.1.6 expired, so that the image on them need to be manually upgraded to 4.1.1.7 and above. You could be running into that issue if the code on an AP is older than that it cannot request, check or upgrade to 4.1.1.7 automatically. You should upgrade all of your platforms manually to 4.1.1.7. The issue should be fixed to check and automatically upgrade after that.