Gamepads only working in devmode

you check syslog for any denials you get when the snap is used in strict mode and a controller is attached ?

I did now, I get these two:

Mar 16 13:25:50 tobias-desktop dbus[7236]: apparmor="DENIED" operation="dbus_method_call" bus="session" path="/org/freedesktop/ScreenSaver" interface="org.freedesktop.ScreenSaver" member="Inhibit" mask="send" name="org.freedesktop.ScreenSaver" pid=11451 label="snap.ppsspp.ppsspp" peer_pid=7494 peer_label="unconfined"
Mar 16 13:25:50 tobias-desktop dbus[7236]: apparmor="DENIED" operation="dbus_method_call" bus="session" path="/org/gnome/ScreenSaver" interface="org.gnome.ScreenSaver" member="SimulateUserActivity" mask="send" name="org.gnome.ScreenSaver" pid=11451 label="snap.ppsspp.ppsspp" peer_pid=7377 peer_label="unconfined"

hmm, clearly unrelated (thats a known issue with teh screensaver inhibition)

do you see different "ALLOWED" lines in syslog when you run it in devmode ?

There's this whole block that didn't appear in strict mode.

Mar 16 13:22:26 tobias-desktop kernel: [16776.042723] audit: type=1400 audit(1521202946.364:267650): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/system/memory/block_size_bytes" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop dbus[7236]: apparmor="ALLOWED" operation="dbus_method_call" bus="session" path="/org/freedesktop/ScreenSaver" interface="org.freedesktop.ScreenSaver" member="Inhibit" mask="send" name="org.freedesktop.ScreenSaver" pid=10666 label="snap.ppsspp.ppsspp" peer_pid=7494 peer_label="unconfined"
Mar 16 13:22:26 tobias-desktop kernel: [16776.100199] audit: type=1400 audit(1521202946.421:267651): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input16/capabilities/ev" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop kernel: [16776.100202] audit: type=1400 audit(1521202946.421:267652): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input16/capabilities/abs" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop kernel: [16776.100235] audit: type=1400 audit(1521202946.421:267653): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input16/capabilities/rel" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop kernel: [16776.100237] audit: type=1400 audit(1521202946.421:267654): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input16/capabilities/key" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop kernel: [16776.100388] audit: type=1400 audit(1521202946.422:267655): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input17/capabilities/ev" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop kernel: [16776.100390] audit: type=1400 audit(1521202946.422:267656): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input17/capabilities/abs" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop kernel: [16776.100417] audit: type=1400 audit(1521202946.422:267657): apparmor="ALLOWED" operation="open" profile="snap.ppsspp.ppsspp" name="/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input17/capabilities/rel" pid=10666 comm="PPSSPPSDL" requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
Mar 16 13:22:26 tobias-desktop kernel: [16776.100429] audit: type=1400 audit(1521202946.422:267658): apparmor="ALLOWED" operation="open" profil...

there you go, the joystick interface needs to allow access to the input device at:

/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card2/input16/capabilities/ev

aaand it looks like https://github.com/snapcore/snapd/commit/82616efcbb4fac3c4a9d2e4846f8ebec7821055b#diff-4a1da2e3f7e118a874d308ec61d7d055 already has the fix in snapd's master tree ...

hmm, in fact https://forum.snapcraft.io/t/joysick-access-for-sdl2-apps/3027/7 says it has been merged into snapd 2.30, that should actually be in use everwhere.

what is the output of "snap version" on your test systems ? i wonder if something regressed here.

First of all thanks for all the help so far, really appreciate it :)
On Fedora the output is
snap 2.31.1-2.fc27
snapd 2.31.1-2.fc27
series 16
fedora 27
kernel 4.15.8-300.fc27.x86_64

Ubuntu
snap 2.31.2
snapd 2.31.2
series 16
ubuntu 17.10
kernel 4.13.0-37-generic

So that fix should be on both systems. I actually came across that same thread and wondered why it was not working.

I happen to have both gamepads available and I can give that a try. For now I'm marking this as confirmed.