This issue is seen when a license key is upgraded or a new license is added using the following CLI command:

root@router> set system license keys <key>.

This causes the BGP sessions to flap with the subsequent loss of traffic till the sessions are re-established again.

BGP flaps and re-establishes after license is added.

Install the license via the "request system license add terminal" command instead of using the "set system license keys key <key>" command.