Wanted to reply to this issue with a more current update.  I was also dealing with my QB crashing when trying to send an invoice (as of April 2021).  I tried all of the suggested fixes posted in all of the forums, including being on call with QB Customer Support for hours.  Someone posted in this forum that they created an invoice with a different template and then they were able to send their invoices.  This was the solution that worked for me.  I created a new basic invoice, without our logo, and was able to send an invoice with no issues.