Device: Aquiring device lock dev_eui=a5b4xxxxxx

today when i send downlink cmd to end device ,i got this problem ,and this problem cause cmd timeout in my platform (AS)
this is log

I want to kown the reason of chirpstack lock downlink cmd over than 15s
any reason ,all of reason

any one help

What exactly is the issue? I do not see any errors only INFO logs.

May be no uplink yet before the very first downlink.