The first “topicList” to be fetched after an initial page load will automatically use the value which was “preloaded” by the server. So, if your theme is calling store.findFiltered before core does, things could get weird.
There were some changes here recently to fix some bugs where the preloaded value wasn’t being used properly, so that might explain the recent regression.
So, workaround is to make your findFiltered call happen after core’s. But… clearly this kind of racing is not by design - we could probably do with some refactoring in core to make this cleaner 