I have just got brand new Meizu M5 note. And everything seems to be fine, except only one thing.
Sim toolkit is not prompting to confirm e-signatures, as we have possibility to sign documents by entering sPIN code to our phones. It shows only for the first time, and that's it.
After restart you can see the prompt for one more time.
Checked SIM card, Moved SIM to other phone. Inserted other SIM to this phone. - IT IS NOT SIM ISSUE
Contacted service provider - everything is fine from their side.
Restored phone to defaults - it is not appearing anymore.
S/W version: 188.8.131.52A - newest, no updates available.
this bug is actually well known and it's unsolved since very early versions of flyme 5. According official flymeos.com forum, for some devices this issue is solved with some latest flyme 6 beta firmware (I don't remember which one). Possible it works also with the stable version. However, for my device (mx4pro) there is no change also with the newest firmware. So you can try to upgrade your firmware to some flyme 6.
If this don't work the only one possibility to solve this issue is to install AOSP Stk.apk instead of installed Meizu version. Of course you can't do it directly, as you'll get shared signature error during the installation process. But if you have Xposed module called Xinstall you can bypass the signature check (it's dangerous and not recommended!) and install it into your system.