As Ramon mentioned, you can duplicate check unsubscription control rule and change logWarning link to logError if (delivery.content.email.length > 1) {logWarning(sg.missingOptoutTextMultivariant(emailContent.variant));}else {logError(sg.missingOptoutText());}  

It totally depends on how many products you have in excel file, if the products count is very less then you can create XF for every product, and in workflow based on the segmentation, you can call those XF in delivery templates. If the products count is high then I feel you can use personalization f...

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Check below post, you need to install SP2 if you are using java8Unable to compile class for JSP: An error occurred at line 95 Please reply back if it is still not resolved.

I am not sure, but in AEM 6.4, we need to move all from etc/designs to /apps/settings/wcm/designs/<projetname>, please move to apps and test.

Yes, recently we have migrated one project from 6.3 to 6.4, you need to move etc/designs to this folder "/apps/settings/wcm/designs/<projetname>" "etc/tags" to "/content/cq:tags""etc/clientlibs" to "project specific clientlibs"

I am not sure about sp2 has any translation related code patch or not we need to check release notes. but you can test this in the local environment by installing SP2 and if everything looks good then only push SP2 into upper environments.

Please replicate video to publish environment and check, if still not appearing then clear cache and try.

Yes, the change will not reflect in live copies. you need to manually move live copies. if the count of the live copies pages is less then you can very well use Move option. if the count of pages in thousands then it is better to write custom rollout configuration. the custom rollout action should i...

There is a good article in HelpX on restructuring check itAdobe Experience Manager Help | Common Repository Restructuring in AEM 6.4