Continuous mode means it ignores the humidity target, not that it ignores the tank. The float switch that stops it when the tank is full is a safety and it always applies.
So the behaviour you are seeing — runs, fills, stops — is exactly what continuous mode does when the tank is not being emptied.
The fix for that is the part nobody mentions in the shop: almost every dehumidifier has a drain hose outlet, usually a small blanked spigot at the back. Fit a hose, run it to a sink, a drain, or out through an airbrick, and the tank stops being the limit. That is what continuous mode is designed to be used with.
Without the hose, continuous mode is close to pointless — you have swapped an automatic machine for one that needs you twice a day.