Some InfoPath form controls, actions, and features require the browser to communicate with the server during a form session. This exchange of data during the session is called a postback, and usually occurs when a form feature has to send data to the server for processing. Unnecessary postbacks impose an additional load on both the browser and the server. To protect the server, a threshold is set for the maximum number of postbacks per session. This limits the number of postbacks that can be executed during a single session when a user is filling out a form, and prevents malicious users from trying to bring down the server.
For SharePoint On-premise following User Session Settings are configurable by Using Central Administration. As Described in http://technet.microsoft.com/en-us/library/cc262263.aspx#authenticate
[Number of postbacks per session] –Default is 75
[Number of actions per postback] –Default is 200
– User Sessions
[Active sessions should be terminated after] -Default is 1,440 Minutes
[Maximum size of user session data]-Default is 4096 Kb
In case of SharePoint Online (a.k.a Office 365 ), these settings are not available in Tenant or SharePoint Admin site . As it is a shared Farm Architecture , they have been set the Default limits as Hard limits to avoid Perf Degradations & prevent DOS Attacks.
If you’re seeing this on your SharePoint Online Deployed Forms , You need to Re-Design your forms to resolve the issues seen . Here is a Blog Series Microsoft’s InfoPath team which are worth a read , providing guidance
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