bluetooth connection to lego boost

[pepo-k]

Hello,
possibly not the right forum to ask, but there could be also clever people to help.

I have a problem to establish a stable connection to lego boost module.
My set-up:
Lego Boost
+
NUC PC D34010WYK with dualboot ubuntu 20.4 and win 10.

Under Win10 I have installed scratch and also scratch link. There I could get connected stable to lego boost and from scratch drive all motors and also optical interface on lego boost.

Under Ubuntu I have installed scratux and also scratch link (as advised on https://pypi.org/project/pyscrlink/).
I can not say if scratux over scratch link is working at all, as my problem starts at very beginning.
When pairing in bluetooth, I get it on, but in a few seconds later is once again off and the lego boost auto-switches off.
Below the output from terminal while trying to connect. And also the output from hci.
Please help me, I can not find the solution by myself.

home@ubuntu:~$ bluetoothctl
Agent registered
[bluetooth]# pair 00:16:53:A5:14:EC
Attempting to pair with 00:16:53:A5:14:EC
[CHG] Device 00:16:53:A5:14:EC Connected: yes
[CHG] Device 00:16:53:A5:14:EC ServicesResolved: yes
[CHG] Device 00:16:53:A5:14:EC Paired: yes
Pairing successful
[CHG] Device 00:16:53:A5:14:EC ServicesResolved: no
[CHG] Device 00:16:53:A5:14:EC Paired: no
[CHG] Device 00:16:53:A5:14:EC Connected: no
[CHG] Controller D8:FC:93:70:00:B6 Discoverable: no
[bluetooth]#

home@ubuntu: hciconfig -a
hci0: Type: Primary Bus: USB
BD Address: D8:FC:93:70:00:B6 ACL MTU: 1021:5 SCO MTU: 96:6
UP RUNNING PSCAN
RX bytes:2592 acl:30 sco:0 events:163 errors:0
TX bytes:6262 acl:26 sco:0 commands:124 errors:0
Features: 0xff 0xfe 0x0f 0xfe 0xdb 0xff 0x7b 0x87
Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
Link policy: RSWITCH HOLD SNIFF
Link mode: SLAVE ACCEPT
Name: 'pepuntu'
Class: 0x1c0104
Service Classes: Rendering, Capturing, Object Transfer
Device Class: Computer, Desktop workstation
HCI Version: 4.0 (0x6) Revision: 0xe00
LMP Version: 4.0 (0x6) Subversion: 0xe00
Manufacturer: Intel Corp. (2)