More than three equals signs make the line disappear, looks like issue with Iosevka SS14

Description of the Issue

With pictures: https://community.notepad-plus-plus.org/topic/22462/npp-dislikes-more-than-three-equals-sign-in-a-row
Additional findings: Bespin is customised with Iosevka SS14 font on this machine.
Iosevka Term SS14 Medium or Iosevka Fixed SS14 medium works.
Iosevka SS14 is working in: TCMD viewer, IBExpert Studio, Delphi 4 IDE, WordPad, Microsoft Word 2007

Steps to Reproduce the Issue

1. Start NPP
2. Change style font to Iosevka SS14 TTF (JetBrains Mono Style) (https://github.com/be5invis/Iosevka/releases)
3. Type something
4. Type four equal signs
5. change font back

Expected Behavior

Nice remark line with brownish background

Actual Behavior

Line disappears

Debug Information

Notepad++ v8.2.1 (32-bit)
Build time : Jan 19 2022 - 18:38:49
Path : C:\Program Files\Notepad++\notepad++.exe
Command Line : "p:****.sql"
Admin mode : OFF
Local Conf mode : OFF
Cloud Config : OFF
OS Name : Windows 7 Professional (32-bit)
OS Build : 7601.24546
Current ANSI codepage : 1250
Plugins : ccc.dll ComparePlugin.dll DSpellCheck.dll HTMLTag_unicode.dll ImgTag.dll mimeTools.dll NppConverter.dll NppExport.dll NppFTP.dll NPPJSONViewer.dll NppQrCode32.dll NppSaveAsAdmin.dll QuickOpenPlugin.dll Tidy2.dll XMLTools.dll _CustomizeToolbar.dll

No source file or test is named. First reproduce the disappearance with Iosevka SS14 TTF and four equal signs, then compare it with Iosevka Term SS14 Medium or Iosevka Fixed SS14 medium; done means the remark line remains visible with the expected brownish background.