Indenting in Python files
After pressing kj cursor goes to the beginning of line
And that's normal behavior
But after I installed plugin it doesn't do this

This seems to be a "bug" in vim. If you type x<BS><Esc> on an empty line you still get the same behavior. Not sure I should work around it in the plugin or fix it in vim.
Please work around it.
:h autoindent
Copy indent from current line when starting a new line (typing <CR> in Insert mode or when using the "o" or "O" command). If you do not type anything on the new line except <BS> or CTRL-D and then type <Esc>, CTRL-O or <CR>, the indent is deleted again.
Please preserve this behavior.
vim-easyescape-plus seems to have a workaround and a nice feature keeping the buf status as unmodified if nothing modified. But unfortunately it doesn't map jk kj simultaneously.
Thank you for the infomation. However, I am not sure how to preserve this behavior. I take a look at vim-easyescape-plus. It will insert a c-w if current only contains <space>. This might be less annoying than the current solution, but it is still not the ideal behavior of autoindent.
I push my workaround. Let me know if it is better.
It is better now. Thank you. How about reverting the modified buffer status? Entering insert mode and doing nothing, a true <Esc> brings back to normal mode with everything intact, while this plugin leaves the buffer modified.
The workaround works great for me! But, it also overwrites the unnamed buffer with whatever whitespace got deleted. Would it be easy to send the whitespace to "_ to avoid that?
Thanks!
Edit: looks like you got that too, thank you!
One lingering problem: after deleting the whitespace, the "." command repeats the delete. Is it possible to run a command without overwriting the . buffer?
I am not sure how to do that since according to the definition of ".", it repeats the last change. This might be possible with https://github.com/tpope/vim-repeat, but I am not really familiar with it.
Since the original question is partially solved, I will close this issue. Let me know if you have better ideas.