Blurred image when using mask

I am trying to use a mask on a models face to lighten one side.

So, creating a mask, selecting 'person' then persons skin and brush, zooming in to 100% the image become blurred and uneditable. Why?

I am running a iMac, 5k 27" retina monitor, 3.4GHz intel i5 processer with 64Gb memory. Radeon Pro 570 4Gb graphics card.

The version of Lightroom details are below.

Lightroom Classic version: 13.1 [ 202312111226-41a494e8 ]
License: Creative Cloud
Language setting: en-GB
Operating system: Mac OS 13
Version: 13.6.4 [22G513]
Application architecture: x64
Logical processor count: 4
Processor speed: 3.4GHz
SqLite Version: 3.36.0
Built-in memory: 65,536.0 MB
Real memory available to Lightroom: 65,536.0 MB
Real memory used by Lightroom: 4,886.5 MB (7.4%)
Virtual memory used by Lightroom: 50,384.7 MB
Memory cache size: 160.1MB
Internal Camera Raw version: 16.1 [ 1728 ]
Maximum thread count used by Camera Raw: 3
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Camera Raw virtual memory: 1083MB / 32767MB (3%)
Camera Raw real memory: 1163MB / 65536MB (1%)
Standard Preview Size: 5120 pixels
Displays: 1) 5120x2880, 2) 1920x1080

Graphics Processor Info:
Metal: AMD Radeon Pro 570
Init State: GPU for Image Processing supported by default
User Preference: Auto

Installed Plugins:
1) AdobeStock
2) Aperture/iPhoto Importer Plug-in
3) Canon Print Studio Pro
4) DxO PhotoLab 2
5) DxO PhotoLab 2 Importer
6) DxO PhotoLab 4
7) DxO PhotoLab 4 Importer
😎 Flickr
9) Helicon Focus Export
10) Nik 6 HDR Efex
11) Nikon Tether Plugin
12) Plugin Parameters
13) Plugin Parameters

Config.lua flags: None

I have to say I do not encounter this problem using other editing software (Capture One)