We have the fix available in the latest release. Please update Illustrator using Adobe Creative Cloud application to the latest build for version Illustrator CC 22.1.
Please refer to our knowledge base FAQ – https://illustrator.uservoice.com/knowledgebase/articles/1844590 if you face difficulty in update.
Or get in touch with us at any of the other support channels – https://helpx.adobe.com/support.html
Ashutosh Chaturvedi | Sr. Quality Engineering Manager – Illustrator
Adobe. Make It an Experience.Harry commented
The Blob Brush is creating a trail of "Ghost cursors" when moved (not applied) that follow the mouse in a line, and because of this glitch there ends up with no size-cursor beneath the brush.
I really like the Blob Brush so this is quite frustrating and visually confusing.
Thank you for reporting the issue. We are able to reproduce it on our end.