Users are being repeatedly prompted to log in and enter verification codes every time they access the Salesforce Sandbox organization, even during the same session or day. This constant authentication requirement disrupts workflow and reduces productivity
2 answers
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It's a new change enforced by salesforce. Please refer the article. It has steps with which you can mitigate the impact
https://help.salesforce.com/s/articleView?id=005220394&type=1
