When I test multiple versions, only 1.5.12 seems to function for me across all of the browsers I use. The most noteworthy part is that the most recent release 1.5.14 also has a bug, despite the fact that I checked more versions (which are detailed here).
It may be important to point out that the importmap is used within an iframe. Perhaps that is relevant given the error message.
Are you able to identify the likely cause and replicate the problem using the information provided?
es-module-shims.js? [sm]:342 Uncaught TypeError: Cannot read property 'head' of null
at HTMLIFrameElement.n.onload
When I test multiple versions, only 1.5.12 seems to function for me across all of the browsers I use. The most noteworthy part is that the most recent release 1.5.14 also has a bug, despite the fact that I checked more versions (which are detailed here).
It may be important to point out that the importmap is used within an iframe. Perhaps that is relevant given the error message.
Are you able to identify the likely cause and replicate the problem using the information provided?