What is the problem with Linux partition?

Question

USB

What is the problem with Linux partition?
I install Linux on a 32GB flash drive and in the process I get such an error, I'm curious because of what it appears, why does it write that the partitions are in use?

Partition(s) 1,2 on /dev/sda have been written, but we have been unable to inform the kernel of the change, probably because it/they are in use. As a result, the old partition(s) will remain in use