Collar Weir Skimmer Basket - Skimmer sucking air

Hi. We have a skimmer with a circular skimmer basket (Certikin HD105) that has a circular "collar" floating weir on the lid. Two issues sometimes occur:

Sometimes in the mornings (when the pump starts up again having been off overnight) we're finding that the skimmer basket is just bobbing about on the water in the skimmer (ie has floated up while the pump was off and isn't seated properly) and so the water is being sucked through the skimmer bypassing the basket.

The other problem we're having is that the floating collar weir seems to sometimes 'float' at its highest point (although if you take it out of the water it moves up and down freely); this means that unless the water level is very high (c. 80% up the skimmer opening), the water sometimes doesn't make it over the weir, leaving the skimmer sucking air and the pump constantly trying to prime. If I manually push the weir under a few times it will eventually settle and behave properly, but often takes several attempts.

These issues don't happen every day, but frequently enough to make me think there's a problem I need to fix - I was thinking maybe I could weight the basket with something to keep it seated (a new chlorine tab keeps it seated), but have no idea about the floating weir problem.

We got the pool with the house and (with help!) have been figuring it out and fixing issues, now all seems fine apart from these skimmer problems. Any help welcome!