Kubuntu screen lock after host OS sleep (screen locking disabled)

I have strange problem: after host OS sleep my Kubuntu guest OS is showing screen unlock prompt though I have disabled screen locking from Kubuntu system settings.
Also the unlock screen proportions are not matching the screen: windows on the desktop are visible on the background and partly possible to interact with.. Interacting with the unlock prompt, however, is difficult:

• the effective location of UI elements are where they should be according to screen not where they are shown
• the password does not unlock desktop, but leaves the system in a state where very few interactions are possible (I guess the same as with the unlock prompt shown), for example terminal does not take input.. shutting down gracefully is impossible.
• the only safe way out from unlock prompt is to shutdown/restart

some kernel logs included, in case it helps..

Any idea how to get rid of this?
BR,
Jani

 

the screenshot of the unlock screen has been cropped, naturally.

 

from kernel log:

Code:

Sep 16 09:08:45 kettu kernel: [  122.453367] WARNING: CPU: 0 PID: 1205 at drivers/gpu/drm/drm_gem.c:1035 drm_gem_object_put+0x42/0x50 [drm]
Sep 16 09:08:45 kettu kernel: [  122.453368] Modules linked in: hid_generic usbhid hid prl_vid(POE) drm_kms_helper syscopyarea crct10dif_pclmul gpio_ich sysfillrect crc32_pclmul ghash_clmulni_intel aesni_intel crypto_simd sysimgblt fb_sys_fops cryptd glue_helper drm psmouse ahci lpc_ich virtio_net libahci i2c_i801 pata_acpi net_failover failover prl_tg(POE)
Sep 16 09:08:45 kettu kernel: [  122.453375] CPU: 0 PID: 1205 Comm: plymouthd Tainted: P           OE     5.4.0-84-generic #94-Ubuntu
Sep 16 09:08:45 kettu kernel: [  122.453376] Hardware name: Parallels Software International Inc. Parallels Virtual Platform/Parallels Virtual Platform, BIOS 17.0.1 (51482) 09/01/2021
Sep 16 09:08:45 kettu kernel: [  122.453381] RIP: 0010:drm_gem_object_put+0x42/0x50 [drm]
Sep 16 09:08:45 kettu kernel: [  122.453382] Code: 8d 78 68 e8 50 65 0f f6 84 c0 74 1e f0 41 ff 0c 24 0f 88 a5 c2 02 00 74 05 41 5c 5d c3 c3 4c 89 e7 e8 d2 f5 ff ff 41 5c 5d c3 <0f> 0b eb de 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 85 ff
Sep 16 09:08:45 kettu kernel: [  122.453383] RSP: 0018:ffff9d50434ffc68 EFLAGS: 00010246
Sep 16 09:08:45 kettu kernel: [  122.453384] RAX: 0000000000000000 RBX: ffff9d50434ffd50 RCX: ffff91f19b0a50c0
Sep 16 09:08:45 kettu kernel: [  122.453384] RDX: 0000000000000000 RSI: ffff91f19b0a50c0 RDI: ffff91f19a179868
Sep 16 09:08:45 kettu kernel: [  122.453385] RBP: ffff9d50434ffc70 R08: ffff91f19b0a50c0 R09: ffff91f1ac007640
Sep 16 09:08:45 kettu kernel: [  122.453385] R10: ffff91f19a478c40 R11: 00000000000004b5 R12: ffff91f19b0a5000
Sep 16 09:08:45 kettu kernel: [  122.453386] R13: 0000000000000000 R14: ffff91f19a179800 R15: ffff91f19b0a4a00
Sep 16 09:08:45 kettu kernel: [  122.453386] FS:  00007ff0008d9740(0000) GS:ffff91f1af400000(0000) knlGS:0000000000000000
Sep 16 09:08:45 kettu kernel: [  122.453387] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
Sep 16 09:08:45 kettu kernel: [  122.453387] CR2: 00007ff0008b3000 CR3: 0000000829f5e004 CR4: 00000000003606f0
Sep 16 09:08:45 kettu kernel: [  122.453388] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Sep 16 09:08:45 kettu kernel: [  122.453388] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

 

someone kicks sddm-greeter running, I'll try to run "journalctl -u sddm" or similar next time..