I see no effects from any updates or slow summer, no decline at all. Sales steady as a rock, same as year before, a bit better actually. Images still top rank in Google also see no effects there.
Big factor is category your in, if your in crowded category's then its probably normal you get mixed results. Summer will probably have some influence, lots of people go on vacation so that will have some impact.
But to the people with multiple accounts I would say look no further, especially those on the two big ones (Turbosquid versus CGtrader), swinging your own clients between these two is a big factor. You can get lower ranking on both sites and influence the Google results, that's probably main reason you see big up and down motions between both accounts successes (your competing against yourself).
Note, you will never rank as high on both platforms then someone serving all clients and direct marketing efforts to here or exclusively on Ts.
Keep in mind there are no special Ts clients, all Ts clients are at same time CGt clients, its only 2 to 3% of people (a small shrinking crowd) that never purchase outside of Ts. Its very few people and not worth swinging own clients for them. You are literally losing money on clients you swing to the 60% account and the risk of lower rankings on both sites and mixed results in Google. If you can add the 60% cut on top of products on Ts then its not that harmful to have an account there, if not, then its just pointless self sabotage.
For a while I even considered making my models on CGt as expensive as on Ts (also add 60% to them to avoid price cut-downs on Ts), but then tell in CGt descriptions people need to use the price offer button to get “guarantee” best price (under the Ts radar). But it just struck me how messed up I can make things for myself, its just not worth it to deal with Ts, its to expensive in every way.