This is such a nebulous issue, each one of you should probably have your own threads because the issue is likely different for each of you. It may be the same, but we don't have enough info to figure it out. Tell us absolutely everything you can about your computer: its specs, exact version numbers of software and OS, security/anti-virus/anti-malware/firewall software and settings, third-party codecs installed, other software installed, and ANYTHING else you can think of about your machine. Then tell us everything you can about your project: format and codec of any footage, any other assets involved, how many layers, what effects are being used, what third-party plugins and scripts you have installed, and ANYTHING else you can think of about your project.
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