I have not been able to replicate it on my side, but some customers have been complaining about the Add to Cart button disappearing (all claims have seemed to be on mobile) after they attach a file to the upload field. Is there something that comes to mind that would cause this? I have received screen recorded videos and multiple claims of it happening.
Would you mind sharing a link or video ..etc and steps to replicate the issue, although I highly doubt it’s related to the plugin as I have never had someone having similar issue.
Sorry, but there don’t seem to be any issue with the plugin, add to cart button is showing fine on the site, you probably have quick buy button plugin that could contribute to this, you may want to disable that and see.
Generally, there is no possible way for the plugin to hide the button as it doesn’t change it’s CSS and doesn’t change WooCommerce templates.