If you're stripping away the old yeast on the bottom that could weight it down, periodically cleaning the vessel, and you have a culture that is still producing I wouldn't be too worried.
The yeast produces CO2, which helps it rise up in the container, but I've also had some brews where the mother sank and didn't come back up. Sometimes it's a matter of ensuring a stable higher temperature for the first couple days of brewing.
If it keeps up and temperature isn't an issue you could purchase and use a bottle of raw kombucha as starter and see if that makes a difference. I like to do that every now and again to keep an interesting colony.
Tap: DIPA, oaked Baltic porter, XXX pale ale, dark IPA
Bottle: vanilla kombucha, oaked puh-er kombucha, blueberry kombucha,
Primary: rose hip kombucha, oaked honey and oolong kombucha, hopped kombucha brewed with green tea infused with cab. grapes