There have been many users reporting trouble updating to 1903, varying from minor malfunctions to major ones, where attempted restore to Windows 1809 has been necessary. Some downloadings and installations have stuck indefinitely, forcing the users to crash their PC's and face the consequences.
My earlier post summarised the situation perfectly.
There is no rush to have 1903, so why take unnecessary risks. There is no reason at all except curiosity and as we all know "curiosity killed the cat".
Let 1903 remain on the shelf for 3 months, more or even to the end of 1809 service life on May 12, 2020. Nothing is lost.
While 1809 is working to perfection, stay with it - If it 'aint broke, don't fix it.
It is widely recommended that an image back-up is made of your existing system before installing 1903.
Macrium Reflect is highly praised for this task.