I'll provide a possible reason the tax rate does not display on the invoice when importing a template.
When importing a customize form template, there's a specific format to follow. I suggest comparing the customized form you're using with the accepted file format. Also, you need to ensure that the fields used to fetch the information on your invoice matches the fields available in the system. This could be the reason the tax rate does not display on the invoice.
If the issue persists, I suggest logging into your QuickBooks account using a private browser (incognito). There are times that the browser keeps outdated Internet files that may cause websites, like QuickBooks Online, to receive an unusually behavior. That being said, Browsing privately is a good way to check issues caused by a full cache.
Use these keyboard shortcuts based on the browser you're using.
For Internet Explorer of Firefox, press Ctrl + Shift + P.
For Chrome, press Ctrl + Shift + N.
For Safari, hold down Command + Shift + N.
If everything looks good, return to your default browser and perform a clear cache. Every so often the cache becomes overwhelmed with older data which can potentially cause viewing and performance issues. Clearing it will refresh the system, and you'll be able to work with a clean slate. However, if the issue continues to occur, try using other supported browsers.