bold writing malfunction

Same thing happened to me, in v19.0. I launched the Creative Cloud app and opened v18.5 and the problem is gone. Therefore I’m assuming it's a bug with v19.0. If you don’t see other versions listed under ‘All apps’ in the CC app, there is guidance here for installing older versions.

Hard to know without seeing it or what exactly is happening.

What font is it? Where did the font come from (client/web/Adobe Fonts/etc.)?
What OS?
What version of InDesign?

Typical fixes in order to try:

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Reinstall the font (delete it from your system and reinstall it)

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If a document is not behaving well then try 

File>Export 

Choose IDML

Open the IDML in InDesign
Save the file as a new InDesign file with a new name
See if the issue persists.

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Try resetting your preferences:

Windows: Start InDesign, and then press Shift+Ctrl+Alt. Click Yes when asked if you want to delete preference files.
macOS: While pressing Shift+Option+Command+Control, start InDesign. Click Yes when asked if you want to delete preference files.
A dialog will appear asking to delete the InDesign Preferences, select 'Yes' on this dialog.
Further info and instructions here if needed:
https://helpx.adobe.com/in/indesign/kb/indesign-preferences-support-file-locations.html

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Reinstalling rarely fixes everything - you can do a complete reinstall using the
Creative Cloud Cleaner Tool https://helpx.adobe.com/creative-cloud/kb/cc-cleaner-tool-installation-problems.html