You can sync your store to BrickOwl, even if you never open for sale on that platform. One thing to check is that the default setting for BL inventory is to delete the lot when the last item sells. Probably want to change that. When I was selling regularly, we tried to keep some slush stock in case of human errors. We'd have a handful left in the bin, but BL deleted the lot because the last one in BL's count was sold, orphaning the remainder. Thankfully we figured that out, which helped.