As per this suggestion
Minecraft Username:
Videowiz92

Brief Description:
Magic Axe effect only works on crimson variant of nether tree, still needs warped variant as well as replanting crimson/warped fungus when stems are broken above dirt/grass/netherrack/nylium.

Instructions:
1. Have magic axe
2. Change axe mode to tree feller or replant mode
3. Hit warped_stem - no results
Also
1. Have magic axe
2. Change axe mode to replant mode
3. Hit crimson/warped stem that is placed above dirt, grass block, netherrack, or crimson/warped nylium - no crimson/warped fungus produced

How many times did you recreate this?:
Many time in nether and in personal farm. Tested on main north.

Result:
Warped stem trees don't get affected by magic axe. Also planting crimson/warped stems above dirt, grass block, netherrack, or crimson/warped nylium blocks and using replant mode will not produce crimson/warped fungus. Also in video test, crimson stem doesn't break above dirt/grass when axe is in replant mode.

Expected Result:
Warped nether tree gets broken down by magic axe as per this suggestion. Replant mode should also produce crimson/warped fungus when harvesting nether trees (both variants.)

Evidence:

 

This seems to have been fixed @andrewkm