<i>When the activation group number as displayed in the call stack (WRKJOB, option 11) changes during execution, but the activation group name does not change; does that mean a new activation group is being initialized.</i>
Yes. Or perhaps more accurately, an new activation group has been created. That assumes that it is in fact the same job, and not just a new invocation of a prestart job.
Quite possibly there was some other step that issued RCLACTGRP ACTGRP(QILE).
If I wanted an activation group to stick around, I would definitely name it something other than QILE. QILE is the standard default from IBM. There’s no predicting what might happen to it.