MTR 4 still have some issues / regressions introduced since MTR 3, which you can help the development of MTR 4 by contributing to such area.

• Train will not render with Sodium in MC 1.19.4 (Or Rubidium on MC Forge 1.20.1, switch to Embeddium in that case)
• Train always open door when stopped with PSD/Platform block, even if it's not a stop in the route (Boardable)
• F3+T when riding a train will kick the player with Invalid move player packet received (Can repo in Singleplayer)
• The resource pack creator cannot use non-alphanumeric characters such as CJK, and characters are garbled when exported.
• Clearing a depot's vehicle while onboard the train will cause the train to continue persist until the player gets off
• Dynamic Texture generation could potentially fail (java.lang.NullPointerException: Cannot invoke “java.awt.Font.deriveFont(int, float)” because “this.font” is null)
• Track signals would get cleared if edited with a brush
• Exception/Crash when loading rail model which points to an non-existent file
• Built-in R-train is lacking some interior model

• Train announcement still gets played even when in-game sound volume is 0
• The model of the player riding train would shake when in F5, while the train render smoothly.

• Sometimes certain train will be completely silent?
• Redstone sensors reportedly not working
• Some mod/environment combination would result in train getting speed up with shaders enabled

• Manual driving (To be reworked after MTR 4.0)
• Ding Sounds in Elevator
• Single Arrival Vertical PIDS

Some of the known problematic shaders are listed below (MTR 4.0.0 beta.16):