Hi there, I just had a similar problem, here is the thread:
Upgrading from pi 3 to pi 4, maybe, what do you think - LibreELEC - LibreELEC Forum
Also if you want to overclock this is what I use on my pi 3 BUT I have found that I do not need to do that anymore every since I updated.
arm_freq=1275
avoid_warnings=1
boot_delay=1
core_freq=500
dtparam=audio=on
initial_turbo=60
gpu_mem=76
h264_freq=333
hdmi_ignore_cec_init=1
over_voltage_sdram_c=4
over_voltage_sdram_p=6
over_voltage=4
sdram_freq=575
sdram_schmoo=0x02000020
temp_limit=85
v3d_freq=500
include distroconfig.txt
Could you post your log please for others to help?