Tendermint version (use tendermint version or git rev-parse --verify HEAD if installed from source): v0.26.0

ABCI app (name for built-in, URL for self-written if it's publicly available): https://github.com/MinterTeam/minter-go-node

Environment:

• OS (e.g. from /etc/os-release): Ubuntu 18.04.1 LTS
• Install tools: -
• Others: -

What happened:
Some proposers create blocks with duplicated transactions. Here is example of a block with 3 exact same transactions: https://pastebin.com/HzzK6myi

What you expected to happen:
Proposers should not duplicate transactions in blocks.

Have you tried the latest version: yes

How to reproduce it (as minimally and precisely as possible): idk :)

Logs (paste a small part showing an error (< 10 lines) or link a pastebin, gist, etc. containing more of the log file): no related logs

Config (you can paste only the changes you've made):
Mempool.CacheSize = 100000
Mempool.Recheck = true
Mempool.Size = 10000

Anything else we need to know:
This issue often appears on slow machines.