How you are using LightGBM?

LightGBM component:

Environment info

Operating System:
Ubuntu 20.04
CPU/GPU model:
Threadripper 1920x
C++ compiler version:
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)
CMake version:
3.16.3
Java version:

Python version:
3.8.5
R version:

Other:

LightGBM version or commit hash:
Version: 3.0.0

Error message and / or logs

@guolinke Have just built it from the latest master branch, still fails. I'll try to separate a minimum reproducible example and create an issue then.

Originally posted by @diditforlulz273 in #2793 (comment)

[LightGBM] [Fatal] Check failed: (best_split_info.left_count) > (0) at /__w/1/s/python-package/compile/src/treelearner/serial_tree_learner.cpp, line 630 .

Traceback (most recent call last):
File "/home/seva/PycharmProjects/ECOM_demand/lgbm_mre.py", line 41, in
model = lgb.train(lgb_params, train_dat, valid_sets=test_dat, verbose_eval=20)
File "/home/seva/PycharmProjects/ECOM_demand/venv/lib/python3.8/site-packages/lightgbm/engine.py", line 252, in train
booster.update(fobj=fobj)
File "/home/seva/PycharmProjects/ECOM_demand/venv/lib/python3.8/site-packages/lightgbm/basic.py", line 2370, in update
_safe_call(_LIB.LGBM_BoosterUpdateOneIter(
File "/home/seva/PycharmProjects/ECOM_demand/venv/lib/python3.8/site-packages/lightgbm/basic.py", line 55, in _safe_call
raise LightGBMError(decode_string(_LIB.LGBM_GetLastError()))
lightgbm.basic.LightGBMError: Check failed: (best_split_info.left_count) > (0) at /__w/1/s/python-package/compile/src/treelearner/serial_tree_learner.cpp, line 630 .

Reproducible example(s)

Archive with code and pickled datasets, 4.5 kb total (lol really a MINIMAL reproducible example)

https://drive.google.com/file/d/1y04Z_11Ce-sETRZPfwjBEBY-aSOMBcHK/view?usp=sharing

Steps to reproduce

1.Run it on lgbm==3.0.0
2. ?????
3. NO PROFIT!
4. Run on lgbm==2.3.1
5.?????
6. PROFIT!