This change, https://hpccsystems.atlassian.net/browse/HPCC-23975 (merged into 7.10.0), introduced a window where the activity could stop and clear an object (iLoader), whilst the serialization code was still using it.
Related - the mergeStats helpers were inadvertently taking a copy of the shared object, and in so doing so linking (and later releasing) - see: HPCC-27606

Combined with this bug, it could cause heap corruption if the serializeStats call was linking as the stop() thread was destroying the object.

Fix is to ensure the iLoader.clear() is inside the critical section.