O LMMS não está iniciando no raspberry pi 4b executando o Ubuntu 21.04

Começou há dois ou três dias. Instalei o Ubuntu 21.04 no meu raspberry pi 4b e instalei o lmms nele. Funcionou bem o suficiente, mas um dia tentei mudar de pulseaudio para jackd2 como servidor de áudio. Reduzi a latência para o mais baixo possível. (Eu mostraria uma captura de tela, mas o lmms gui não está funcionando.) Ele mostra a tela de inicialização, mas agora não mostra o gui. Às vezes, uma janela de erro aparece dizendo "o Ubuntu tem um erro interno" e outra diz "lmms fechado inesperadamente". Não faz isso toda vez que tento; às vezes não mostra nada. Ele simplesmente não abre o gui. Eu tentei iniciar o lmms via terminal, e estes são os logs de erro que ele produziu.

pi@pi-raspberrypi:~$ lmms
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
Notice: could not set realtime priority.
Cannot connect to server socket err = Connection refused
Cannot connect to server request channel
jackdmp 1.9.17
Copyright 2001-2005 Paul Davis and others.
Copyright 2004-2016 Grame.
Copyright 2016-2021 Filipe Coelho.
jackdmp comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
JACK server starting in realtime mode with priority 10
self-connect-mode is "Don't restrict self connect requests"
audio_reservation_init
Acquire audio card Audio0
creating alsa driver ... hw:0|hw:0|1024|2|48000|0|0|nomon|swmeter|-|32bit
ALSA: Cannot open PCM device alsa_pcm for capture. Falling back to playback-only mode
configuring for 48000Hz, period = 1024 frames (21.3 ms), buffer = 2 periods
ALSA: final selected sample format for playback: 16bit little-endian
ALSA: use 2 periods for playback
Cannot use real-time scheduling (RR/10) (1: Operation not permitted)
AcquireSelfRealTime error
Cannot use real-time scheduling (RR/5) (1: Operation not permitted)
JackClient::AcquireSelfRealTime error
JackEngine::XRun: client = lmms was not finished, state = Running
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
JackEngine::XRun: client = lmms was not finished, state = Triggered
JackAudioDriver::ProcessGraphAsyncMaster: Process error
Destination port in attempted (dis)connection of system:playback_2 and  is not an input port
Segmentation fault (core dumped)
pi@pi-raspberrypi:~$ Destination port in attempted (dis)connection of system:playback_2 and  is not an input port
JackGraphManager::Disconnect: port_src = 10 not used name = 
Input port index = 10 not found for application ref = 2
Unknown error...
terminate called after throwing an instance of 'Jack::JackTemporaryException'
  what():  

Eu reinstalei o lmms de duas maneiras diferentes, como usar snap via terminal, snap via sotre snap e snap via terminal apt e ele tem o mesmo problema. Sabe o que pode ser feito para corrigi-lo? Parece que tem algo a ver com um conector mal instalado. Eu tentei reinstalar todos os pacotes jack, libjack e jackd que pude encontrar, mas nenhuma correção ainda.