I think we can rule out the GA-import as the last day of imported data was May 26th and the archiving memory usage increase starts with May 27th.
Here a sample visit log from May 27th:
From that it looks like the tracking of things like SKU data (and product name) per product page impression (see arrow towards the hover popup) seems to be a size issue as we have hundreds of thousands of those in a comparatively short amount of time of those.