Which route do you use to make conference calls @Ranaping ?
i.e an app etc ?
If so make sure all apps are also updated and that the developer hasn't reported an issue clash with the new update.
You can also try clearing it's cache files.
And clear the phone's cache files via > Clear Cache Files from the phone's System Partition Section > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too.
Check with your network they still offer conferencing calls.
If I can be of any further help then please don't hesitate. Take care. 😎