Hey agastelum,
Thanks for writing in! Sorry to hear about the issues you’re having updating your plugins. I’m afraid that since this is affecting all plugins on your end, that it may be an indication of a larger issue, which is not limited to just the MailChimp List Subscribe Form plugin. Because of this, this issue is outside of our range of support that we provide here, and it will ultimately require some further testing in the local environment.
As a general recommendation (if you haven’t already), it might be a good idea to try and isolate what’s causing the issue by removing potential factors from your setup. For example, try disabling all active plugins on your site, then doing the update once again. Additionally, try reverting to one of the default WordPress themes (or a stable, basic one) and then try updating again. If you’ve made any changes to the code of anything on your site, then try rolling those changes back if possible, to see if that resolves the issue. And finally, you may find more in-depth answers on other forums outside of just this plugin, so I encourage searching through the more general WordPress forums for similar reports and additional troubleshooting steps that may be available.
-tk
