Midi output is an octave lower than it should be.

[qwertyozo]

When i get any instrument plugin and send its midi output to a synthesizer on my computer (running LMMS 1.2.0 rc6 on Win 10)
the output sound is always an octave lower than the input, even if the base note is changed.

[musikbear]

When i send midi output to a synthesizer, the output sound is always an octave lower than the input, even if the base note is changed.

That must be a setting on your hardware midi synth. I am sure you have an octave setting ...some dial showing +/- 1, 2, 3.. maby more, but study your synth' manual, and look for something like 'Setting octaves'
The only way to change octaves in lmms is the base-note (correct way), and changing the master-pitch (wrong way)

(eg the slider left of CPU-meter)
Check your master-pitch!

Besides that, since you are new in Forum
Welcome to the forum qwertyozo !
Here are all important links:
http://lmms.io/forum/viewtopic.php?f=1&t=4740
-A few rules and useful forum instructions

[zonkmachine]

This is a known issue: https://github.com/LMMS/lmms/issues/1857