I also have this problem with a 770 GTX since I switched to KDE 5 about 5
months ago. Freeze without reason learns exept the mouse cursor. 
Kubuntu 17.10, Kubuntu 18.4, Debian 9 KDE and KDE Neon, same problem. In
addition, with the nVidia driver it's worse.

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01:00.0 VGA compatible controller: NVIDIA Corporation GK104 [GeForce GTX 770]
(rev a1) (prog-if 00 [VGA controller])
        Subsystem: Micro-Star International Co., Ltd. [MSI] GK104 [GeForce GTX
770]
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort-
<MAbort- >SERR- <PERR- INTx-
        Latency: 0, Cache Line Size: 64 bytes
        Interrupt: pin A routed to IRQ 27
        Region 0: Memory at f6000000 (32-bit, non-prefetchable) [size=16M]
        Region 1: Memory at e8000000 (64-bit, prefetchable) [size=128M]
        Region 3: Memory at f0000000 (64-bit, prefetchable) [size=32M]
        Region 5: I/O ports at e000 [size=128]
        Expansion ROM at 000c0000 [disabled] [size=128K]
        Capabilities: <access denied>
        Kernel driver in use: nouveau
        Kernel modules: nvidiafb, nouveau

01:00.1 Audio device: NVIDIA Corporation GK104 HDMI Audio Controller (rev a1)
        Subsystem: Micro-Star International Co., Ltd. [MSI] GK104 HDMI Audio
Controller
        Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort-
<MAbort- >SERR- <PERR- INTx-
        Latency: 0, Cache Line Size: 64 bytes
        Interrupt: pin B routed to IRQ 17
        Region 0: Memory at f7080000 (32-bit, non-prefetchable) [size=16K]
        Capabilities: <access denied>
        Kernel driver in use: snd_hda_intel
        Kernel modules: snd_hda_intel