This is completely normal in the process of mining withe current state of the stratum protocol

After a block was found you need some seconds to build a new block template and transmit it to all the miners. In the meantime miners are using an empty block template so that the asics don’t have to stop working. If a block is found in this small amount of time an empty block will be added to the chain.

It’s not the result of mean miners who don’t want to add transactions to the block. It’s a technical problem that will be fixed with the new stratum v2 protocol