Created attachment 142336 [details]
backtrace of plasmashell process

Same problem here using Fedora 29 rpms. Backtrace attached.

Device: NV44 GeForce 6600 LE 512MB DDR2

System: Fedora 29 x86_64
Mesa DRI drivers: 18.2.2-1.fc29
Nouveau: 1.0.15-6.fc29
Plasmashell: 5.13.5-1.fc29