for G Suite / Office 365
This occurrence can be caused by the complicated search conditions that have been set, especially if the customer has fairly large amount of emails in Archive. The search engine will take longer time to process when multiple and complicated conditions are being set. As a result, the session reach timeout period before receiving the search result.
To avoid the issue above, please shorten the search time period and reduce the search conditions in order for the search engine to process faster.
In addition, searching by the keyword contains in email body can take a while. We recommend you to shorten the time period when making a search by this criteria.