@Loopty Thank you for verifying this.
Every mod specifies a stable version, so a beta or alpha version might cause problems.
For example, if you use the beta version of IMT, you will get errors in road placement.
If you don't have Prop, etc., you will get missing or errors in LSM, but you can ignore them except for visual issues.
If you place a road and there are no simulation errors or other fatal problems, you are probably fine.

Yes, not all assets were installed. But the problem still persisted.
Error appears when I select road in the list, but if I build it, it seems to look fine.

Probably a bug due to alpha version AN (other mods require alpha)

@Loopty
Do you have the necessary mods and assets installed?
Please check this collection.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2896825380

Or make sure you are not using old or incompatible mods.
If you want to check the compatibility of a mod, you can easily do so using the Compatibility Report V2.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2881031511

Array index is out of range. [System.IndexOutOfRangeException]

Details:
No details

@AnotherGuy The IMT line style specifies the Prop of the bollard in vanilla.
Please check the line style from IMT to see how it is set up.

can share how you add the bollard on the lane for separate both lane?