This is a query I got a while ago. It was regarding why after an ISSU upgrade in a DC stack switch role switched over. So Why SW1 became secondary and SW2 became active. This was in regards to 9500 series switches.
Rest assured this behaviour is "normal".
According to Cisco's documentation:
"The standby switch is provisioned with the new software and it reloads with the new software version. Next, the active switch is provisioned with the new software and it reloads. The standby switch with the new image now becomes the active switch and the old active switch becomes the standby."
So its normal for the standby to become the active and the active to become the standby. The active switch controls both the switches of Cisco StackWise Virtual.
The stack priority in this case does not matter because ISSU is forcing the standby to become active. This is to prevent Dual-Activation as you don't want both switches to become active-active at the same time, as that will cause issues. Priority only happens during election. Since its already become active, it wont be doing this election again. Election usually only happens during another restart. It is not like HSRP for example which has pre-emption. It wont auto change.
If you want the primary (SW2) to go back to being secondary you will have to ensure another election happens again.
This link provides more information: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/17-9/configuration_guide/ha/b_179_ha_9500_cg/configuring_issu_on_stackwise_virtual.html
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