Flatpak: can't start any apps error: "Failed to install open(O_TMPFILE): Permission denied"

[Mek101]

Hi, every time I try to either install or run a flatpak application I get the error that I don't have permissions to 'open(O_TMPFILE)'
Eg:

Code: Select all

mek101@mint19-desktop:~$ flatpak install flathub com.abisource.AbiWord
Remote ‘flathub’ found in multiple installations:
1) system
2) user
Which do you want to use (0 to abort)? [0-2]: 2
Installing in user:
com.abisource.AbiWord/x86_64/stable        flathub 05c536c07d1e
  permissions: ipc, network, wayland, x11
  file access: home
  dbus access: ca.desrt.dconf, org.gtk.vfs.*
  tags: stable
com.abisource.AbiWord.Locale/x86_64/stable flathub 029ab322e4ba
Is this ok [y/n]: y
Installing for user: com.abisource.AbiWord/x86_64/stable from flathub
error: Failed to install com.abisource.AbiWord/x86_64/stable: open(O_TMPFILE): Permesso negato

Code: Select all

mek101@mint19-desktop:~$ flatpak run com.leinardi.gwe 
error: open(O_TMPFILE): Permesso negato

However, if I run the commands with 'sudo', install works, and running an application starts but no window or terminal output show up.
I may have to point out that I also had problems with compiling V (https://github.com/vlang/v/issues/4649) because I didn't have the permissions to access '/var/tmp/tcc', and I solved them by using '/tmp/tcc' instead.
Does flatpak also use '/var/tmp' perhaps? It's as it should be or is my system to have messed up permissions?