The bug
I noticed that after reloading the world, my resistance 255 effect wasn't working, in fact, after i checked, its amplifier reset to 0.
Steps to reproduce
Give yourself an effect which amplifier is greater than 127
Reload the world
Do
/data get entity @s ActiveEffectsNotice how the effect amplifier is 0
Possible cause
This might have to do something with how signed bytes work.
Because we're entering unsigned bytes (0->255) in the /effect command as the amplifier, but the amplifier tag itself is a signed byte (-128->127), the game writes a negative value to the amplifier.
So, 128 is -128, 200 is -56 and 255 is -1.
However, when the game checks the amplifier, and sees the negative amplifier, it treats it as 0.
Environment
java -version statistics:Java version "1.8.0_171"Java(TM) SE Runtime Enviroment (build 1.8.0_171-b11)Java HotSpot(TM) 64-bit Server VM (build 25_171-b11, mixed mode)
Windows 8.1 64-bit
AMD A8 Processor with AMD Radeon R5 graphics 2.20 GHz
Not completely same with MC-108704, more likely a relative ticket.