I think the primary culprit is the power management on both the host and client I have an MX Master and a K380. The MX Master has a noticeable lag in Bluetoot

I think the primary culprit is the power management on both the host and client I have an MX Master and a K380. The MX Master has a noticeable lag in Bluetooth and both will have a noticable delay when first used after a period of inactivity before springing to life. The K380 seems to have a key buffer to mitigate the delay. If however I have my Bluetooth headphones powered on and active to the host, keeping the bt radio active, most of the issues go away.