Also experiencing this bug. Freshly installed 18.04 on Acer N2620G thin client (Celeron 887/i915). Have upgraded system to latest release. Experiencing minor anomalies in video.

[   17.595601] ------------[ cut here ]------------
[   17.595603] Could not determine valid watermarks for inherited state
[   17.595695] WARNING: CPU: 1 PID: 300 at /build/linux-UDHJtG/linux-4.15.0/drivers/gpu/drm/i915/intel_display.c:14537 intel_modeset_init+0xfcf/0x1010 [i915]
[   17.595696] Modules linked in: btintel i915(+) wmi_bmof bluetooth arc4 snd_seq_midi snd_seq_midi_event rtsx_pci_ms ecdh_generic serio_raw drm_kms_helper ath9k ath9k_common ath9k_hw snd_rawmidi memsti$
[   17.595727] CPU: 1 PID: 300 Comm: systemd-udevd Not tainted 4.15.0-96-generic #97-Ubuntu
[   17.595729] Hardware name: Acer Veriton N2620G/Veriton N2620G, BIOS P21-A3 01/09/2013
[   17.595786] RIP: 0010:intel_modeset_init+0xfcf/0x1010 [i915]
[   17.595788] RSP: 0018:ffffbae000b2b9b0 EFLAGS: 00010286
[   17.595790] RAX: 0000000000000000 RBX: ffff945b970f0000 RCX: 0000000000000006
[   17.595792] RDX: 0000000000000007 RSI: 0000000000000096 RDI: ffff945b9f316490
[   17.595793] RBP: ffffbae000b2ba40 R08: 000000000000033c R09: 0000000000000004
[   17.595794] R10: 0000000000000040 R11: 0000000000000001 R12: ffff945b927f8000
[   17.595796] R13: ffff945b91fa9000 R14: 00000000ffffffea R15: ffff945b970f0358
[   17.595798] FS:  00007fe153334680(0000) GS:ffff945b9f300000(0000) knlGS:0000000000000000
[   17.595799] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   17.595801] CR2: 00007ff7212f6080 CR3: 00000001179e4005 CR4: 00000000000606e0
[   17.595802] Call Trace:
[   17.595854]  i915_driver_load+0xa73/0xe60 [i915]
[   17.595900]  i915_pci_probe+0x42/0x70 [i915]
[   17.595905]  local_pci_probe+0x47/0xa0
[   17.595908]  pci_device_probe+0x10e/0x1c0
[   17.595913]  driver_probe_device+0x30c/0x490
[   17.595916]  __driver_attach+0xcc/0xf0
[   17.595919]  ? driver_probe_device+0x490/0x490
[   17.595922]  bus_for_each_dev+0x70/0xc0
[   17.595924]  driver_attach+0x1e/0x20
[   17.595927]  bus_add_driver+0x1c7/0x270
[   17.595929]  ? 0xffffffffc0b42000
[   17.595932]  driver_register+0x60/0xe0
[   17.595933]  ? 0xffffffffc0b42000
[   17.595936]  __pci_register_driver+0x5a/0x60
[   17.595994]  i915_init+0x5c/0x5f [i915]
[   17.595998]  do_one_initcall+0x52/0x19f
[   17.596001]  ? __vunmap+0x8e/0xc0
[   17.596005]  ? _cond_resched+0x19/0x40
[   17.596008]  ? kmem_cache_alloc_trace+0xa6/0x1b0
[   17.596012]  ? do_init_module+0x27/0x213
[   17.596015]  do_init_module+0x5f/0x213
[   17.596019]  load_module+0x16bd/0x1f20
[   17.596024]  ? ima_post_read_file+0x96/0xa0
[   17.596028]  SYSC_finit_module+0xfc/0x120
[   17.596031]  ? SYSC_finit_module+0xfc/0x120
[   17.596035]  SyS_finit_module+0xe/0x10
[   17.596038]  do_syscall_64+0x73/0x130
[   17.596042]  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[   17.596043] RIP: 0033:0x7fe152e50839
[   17.596045] RSP: 002b:00007fffa59e2a58 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
[   17.596047] RAX: ffffffffffffffda RBX: 0000561b71253950 RCX: 00007fe152e50839
[   17.596049] RDX: 0000000000000000 RSI: 00007fe152b2f145 RDI: 0000000000000015
[   17.596050] RBP: 00007fe152b2f145 R08: 0000000000000000 R09: 00007fffa59e2b70
[   17.596051] R10: 0000000000000015 R11: 0000000000000246 R12: 0000000000000000
[   17.596052] R13: 0000561b71244a80 R14: 0000000000020000 R15: 0000561b71253950
[   17.596054] Code: e9 46 fc ff ff 48 c7 c6 f7 0d ad c0 48 c7 c7 4f 01 ad c0 e8 94 b6 a4 de 0f 0b e9 73 fe ff ff 48 c7 c7 40 66 ae c0 e8 81 b6 a4 de <0f> 0b e9 4b fe ff ff 48 c7 c6 04 0e ad c0 48 c7 c7$
[   17.596081] ---[ end trace 815509aa975c831e ]---
[   17.602180] [drm] Initialized i915 1.6.0 20171023 for 0000:00:02.0 on minor 0
[   17.602401] [Firmware Bug]: ACPI(GFX0) defines _DOD but not _DOS

playaspec@Acer-N2620G:~$ cat /proc/version
Linux version 4.15.0-96-generic (buildd@lgw01-amd64-004) (gcc version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)) #97-Ubuntu SMP Wed Apr 1 03:25:46 UTC 2020