welcome to the notepad++ community, @Peter-Gründler
this does not seem to happen to me, using notepad++ 7.6.6 32 bit and dspellcheck 1.4.11.0.
if i switch to round box, and right-click on any misspelling and choose ignore for current session, only the highlight of this word is removed, but not all.
maybe the author @Predelnik has an idea what could cause this, or you can have a look at the issue tracker, if something similar has been reported already:
https://github.com/Predelnik/DSpellCheck/issues
what dspellcheck version are you using, and what is your debug information from the notepad++ menu: ? > debug info... > copy debug info into clipboard ?
the debug info of the machine i’ve just tested this is:
Notepad++ v7.6.6 (32-bit)
Build time : Apr 3 2019 - 23:49:50
Path : C:\Program Files (x86)\Notepad++\notepad++.exe
Admin mode : OFF
Local Conf mode : OFF
OS : Windows 7 (64-bit)
Plugins : ComparePlus.dll dbgpPlugin.dll DSpellCheck.dll ElasticTabstops.dll EmmetNPP.dll HexEditor.dll IndentByFold.dll JSMinNPP.dll LuaScript.dll MarkdownViewerPlusPlus.dll mimeTools.dll NavigateTo.dll NppAutoIndent.dll NppConverter.dll nppcrypt.dll NppExport.dll NppFTP.dll NppJumpList.dll NppMarkdownPanel.dll NppSnippets.dll NppTextFX.dll NppUISpy.dll PreviewHTML.dll PythonScript.dll SourceCookifier.dll Tidy2.dll XMLTools.dll
best regards.