Lightroom Classic 12.01 Updates

Sure.

Lightroom Classic version: 12.0.1 [ 202210260744-9e008017 ]
License: Creative Cloud
Language setting: en
Operating system: Windows 10 - Home Premium Edition
Version: 10.0.19045
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 4.0GHz
SqLite Version: 3.36.0
CPU Utilisation: 0.0%
Built-in memory: 24538.6 MB
Dedicated GPU memory used by Lightroom: 184.2MB / 8081.0MB (2%)
Real memory available to Lightroom: 24538.6 MB
Real memory used by Lightroom: 13964.4 MB (56.9%)
Virtual memory used by Lightroom: 15659.8 MB
GDI objects count: 822
USER objects count: 2652
Process handles count: 16013
Memory cache size: 1811.5MB
Internal Camera Raw version: 15.0 [ 1261 ]
Maximum thread count used by Camera Raw: 5
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Camera Raw virtual memory: 8364MB / 12269MB (68%)
Camera Raw real memory: 8344MB / 24538MB (34%)
System DPI setting: 120 DPI
Desktop composition enabled: Yes
Standard Preview Size: 2560 pixels
Displays: 1) 2560x1440, 2) 1920x1080
Input types: Multitouch: No, Integrated touch: No, Integrated pen: No, External touch: No, External pen: No, Keyboard: No

Graphics Processor Info:
DirectX: NVIDIA GeForce GTX 1070 (31.0.15.2698)
Init State: GPU for Export supported by default
User Preference: Auto

Application folder: C:\Program Files\Adobe\Adobe Lightroom Classic
Library Path: Z:\Lightroom\Lightroom Catalog-2-v12-2.lrcat
Settings Folder: C:\Users\MINGHUI\AppData\Roaming\Adobe\Lightroom

Installed Plugins:
1) AdobeStock
2) Flickr
3) Nikon Tether Plugin

Config.lua flags: None

Adapter #1: Vendor : 10de
Device : 1b81
Subsystem : 37011458
Revision : a1
Video Memory : 8081
Adapter #2: Vendor : 1414
Device : 8c
Subsystem : 0
Revision : 0
Video Memory : 0
AudioDeviceIOBlockSize: 1024
AudioDeviceName: $$$/dvaaudiodevice/SystemDefaultAndEffectiveDeviceName=System Default - Speakers (High Definition Audio Device)#{comment}DVAAU-4201250: Open the audio hardware preferences page.
AudioDeviceNumberOfChannels: 2
AudioDeviceSampleRate: 48000
Build: LR5x19
Direct2DEnabled: false

Tried, still happening. Before the updates, had no such issues with lightroom classic running with HDR Merge while doing other work at the same time.

When you attempted the merge, did you go thru the "normal" process of selecting the photos, starting the merge, and getting the preview, then selecting various settings like ghost, etc. Or, did you use the shortcut to skip the preview stage?