You can prevent or fix this error by making sure that you only have four Salesforce data sources that use one Salesforce user account to authenticate. If you increase the number of data sources more than this, then the authentication of the earliest data source you have is revoked. The authentication of the newer data source replaces the earliest's.
Panoply integrates with Salesforce as an OAuth-enabled connected app. Salesforce limits a connected app to five unique approvals per user account. Salesforce's documentation on managing OAuth-enabled connected apps details this rule.
Each authenticated data source in your Panoply account is recognized by Salesforce as one individual approval. So if you have four data sources that use one Salesforce account, that's four approvals already. It maxes out to five because you'll have to factor in the current web session too.
If you need additional Salesforce data sources, you must use other Salesforce accounts to authenticate the data sources.