Sign Up link not opening sign up form

For the first problem, it could be a permalink issue, although it worked fine for me with both desktop and my phone.
Sometimes you need to flush the permalink cache by going to your WordPress permalinks settings page and just hitting save (don’t need to change anything).

Otherwise, the most likely cause is caching of the page, either by the browser or a caching plugin you have, or possibly some server side caching (would have to ask your hosting provider about that).

Another smaller possibility is some conflict where some other plugin, theme, or script, is rewriting the URL arguments, or somehow removing some of the arguments. When the problem occurs do you still see that last 2 arguments with the task ID and date in the URL in the browser address bar? They should look something like this:
&task_id=523&date=2022-09-07
If those are missing, then it will just go back to the sheet page. Those two arguments need to be set for my plugin to show the signup form.

For the Customizer update issue, check to see that the license is the same, or if it got changed if you let the old one expire. The most likely cause, if it has been a long time since you updated, is that changes in the licensing software I use are not working with your old version. In any case where you have trouble updating through the dashboard, you can always login to your account on my site and download the zip file of the newest version (as long as you have an active license), and then you can update from that. Recent versions of WordPress allow you to update a plugin by simply uploading the newer version zip file just like you are installing a new plugin. Go to the plugins page, select Add New, choose the option to upload, then upload the zip file. Then WordPress will show you a comparison of the old version and the new version (just version numbers) and ask if you want to replace the old/current version with the uploaded version… just confirm that, and you’re good to go.