In my recent Dynamics 365 for Operations implementation on 7.1, we encountered an issue with MPOS switching to offline randomly . MPOS as we know switches to offline either when triggered manually or when the switch is seamless (automatically) when there is any issue in the communication between MPOS and D365 Retail Server, an example is a network interruption (for more information on the overall Retail Topology do refer this link MPOS Technical Architecture)
In a usual scenario, when an interruption occurs in between a transaction, cashier would get an error message the Cart State has changed. The cashier would need to void the transaction and then start all over again and end with creating an offline transaction (Not the kind of experience you want when you have a queue of customers at the billing). Another issue that coupled with this was that the MPOS logo would not switch from offline to online when the MPOS mode switched.
Make sure you uptake following binary hotfixes as soon as you can if you have enabled MPOS in offline mode
KB 4049328 – MPOS offline logo issue
KB 4058723- Set of reliability fixes for POS Offline
Also include the following X++ hotfix which complements the above binary fix
KB4058724 – Set of reliability fixes for POS Offline