Sandspider

I just recently upgraded some things on my mountain bike (listed below in case its not important). Now when I shift to the lowest gear in the front the chain sticks at the bottom and wraps all the way around and locks up. In other words, where the chain usually falls off the cog at the bottom, to move towards the rear derailer, it sticks instead and wraps around the cog until it jams. Hope that makes sense. Also all other gears work fine as long as i am not in the lowest front gear.

Here are my recent relavent changes: New rear derailer, 9 speed cassete, 9speed chain, (was previously 8 speed).

bkaapcke

Has that small chainring had lots of use? If so, I suspect that it's worn out. A worn ring (fish hooked teeth) and a new chain may have the teeth holding on to the chain pins long enough to create this problem. Even more likely with an aluminum front gear. Have a close look at the teeth from the left side of the bike. bk

Al1943

It's called chain suck.
Good advice above. Also check the chain for a tight link, a link that the plates don't rotate around the pin well.
Check the chain for stretch. When a foot of chain has stretched to 12 1/16 inches it should be replaced.

MudPie

For a good read about chain suck: https://www.fagan.co.za/Bikes/Csuck/