Recently I upgrade my pi 3 to 4 and installed Lakka 2.3.1. I am able to connect and use my bluetooth keyboard until I reboot or shutdown the system. I did have this working on a previous version maybe 2.2.2 but I don’t have the image to reflash and test on my pi 3. I have tried the current nightly (2019-11-04.img.gz) and an older one (2.2-devel-20190723103245-r28318-g021d545641.img.gz). Both of which connect but also doesn’t reconnect upon reboot.
I found out it does save, but in order for me to connect the keyboard, I have to power it on and off about five times.