If your Gmail and Corporate email are working fine then the issue cannot be iOS update.
I have a passion and hobby to go through complete literature and review of all iOS and needless to say I haven't missed iOS 12.1.3 & 12.1.4 assessment published on various news media and on Apple web page including leading news magazines (Forbes).
No where I could find any link on the problem faced by you. Introspect and have a complete and thorough check on the way you handle settings on your iPhone.
Read often for a peaceful & stress free life.
Nevertheless try checking the following on your iPhone (See the Two pics below for better understanding)
Setting > Password & Accounts > [Tap on the account which is not synching] > Mail [Enable]


Add an email account to your iPhone, iPad, or iPod touch - Apple ...
https://support.apple.com/en-in/HT201320