Ubuntu freezes or is very slow because RAM memory and Swap are overloaded

[J-Paul BERARD]

I use BOINC and sometimes my computer freezes (the mouse don't move anymore, no answer to the keyboard) or become very slow.
Today I reached to run System monitor and I saw the ram (8 Go) and the swap file were fulled up !
I reached to stop the BOINC Daemon, and recovered the memory.
Beside Boinc, I was using Firefox (webpage without video) and Thunderbird.
In Boinc-manager, the memory allowed was 75 % when the computer is busy and 90 % when it is not busy.

Isn't to the system to manage the RAM to prevent to be overloaded ?
Is it a bug of Boinc-client ?

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: boinc-client 7.16.6+dfsg-1
ProcVersionSignature: Ubuntu 5.4.0-29.33-generic 5.4.30
Uname: Linux 5.4.0-29-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Sun May 17 20:09:36 2020
InstallationDate: Installed on 2020-04-10 (37 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Beta amd64 (20200402)
SourcePackage: boinc
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.boinc-client.gui_rpc_auth.cfg: [inaccessible: [Errno 13] Permission non accordée: '/etc/boinc-client/gui_rpc_auth.cfg']
mtime.conffile..etc.boinc-client.global_prefs_override.xml: 2020-05-17T12:06:06.427110