On my environment with Microsoft 365 apps installed, I could not reproduce your issue.
Could you please share us which version of Office are you using now?
How did you instert the bullet icons?
Which type of file did you use mail merge to create? Such as letters, Labels.
Let me show you my test details.
Following image is the data source of recipients.
I start the mail merge for letters, then I click "Step-by-Step Mail Merge Wizard. The recipients are as image below.
I write the letters as following, the bullet points are inserted via the Bullets icon from Home tab > Paragraph group.
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If you preview the results, you would find the bullet point would not appear if the field has no data.
Any questions, you may psot back.
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