@CammackIT Has the MX not been configured with full tunnel to VPN hub which could have been adding additional latency to Internet traffic including Saas application (Office365) access? If it had been configured as full tunnel, changing it to split tunnel (Untick of default route to VPN hub) would reduce latency much. In addition, setting up traffic shaping for Productivity > Windows Office 365 as high priority and shape non-business critical application such as streaming Youtube, gaming etc would give priority for business critical application and Office365 application. If stability does not stay even the above is configured and it has been configured as split tunnel (Direct internet access), isolating issue if it was cased by high latency or delay response of HTTP(S) to application would be an idea to troubleshoot it. (Meraki Insight provides more visibility and troubleshooting for Saas application including Office365 though) Hope this would help some!
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