The default value of the mac-persistence-timer has been changed from 10 minutes to 20 minutes on QFX5K series switches, excluding the QFX5100 model.
This KB article explains the details of this behavior change.

The mac-persistence-timer is used to manage the system MAC address, which can serve as the base MAC address for IRB and LAG interfaces.
When an FPC is removed from a Virtual Chassis(VC) and the system MAC address was originally derived from that FPC, the timer starts. Once the timer expires, the system MAC address is updated.
If the removed FPC rejoins the VC before the timer expires, the system MAC address remains unchanged.

When the system MAC address is updated, LACP and IRB interfaces will flap to reflect the new MAC address, potentially causing disruptions.

Although technical documentation may still state the default timer as 10 minutes, it is actually 20 minutes on QFX5K series switches.

This change was made because the original 10-minute timer was insufficient during the NSSU (Non-Stop Software Upgrade) process. In such cases, the FPC may not come back online within 10 minutes after a reboot, causing the timer to expire and triggering interface flaps. This can lead to L3 traffic loss.
This default timer has been changed to 20 minutes from 19.2R2 and later versions.
It is strongly recommended to configure the mac-persistence-timer to 20 minutes or higher, or disable on QFX5K series switches to avoid such issues.

set virtual-chassis mac-persistence-timer 20
or
set virtual-chassis mac-persistence-timer disable