bug:SSM Package Incorrectly Assigned in Model Splitter

[vharilal025]

Describe the bug
I was trying to run a seawater intrusion model simulation using MODFLOW 6.
In my setup: The left boundary represents freshwater inflow, modeled using the Well (WEL) package.
The right boundary represents tidal fluctuations, simulated using the General-Head Boundary (GHB) package.
When using mf6split.split_multi_model() to divide the model into subdomains, the Sink and Source Mixing (SSM) package does not correctly update source/sink assignments in the split models.

After splitting, the left model should retain only the WEL package, and the right model should retain only the GHB package.
Actual Behavior: The right model incorrectly contains WEL, and the left model incorrectly contains GHB, even though these boundary conditions should belong to separate subdomains.
This leads to errors like flow package cannot be found in each model as

ERROR REPORT:

  1. Flow package cannot be found: GHB-1

UNIT ERROR REPORT:

  1. Error occurred while reading file 'trans_0.ssm'

and

ERROR REPORT:

  1. Flow package cannot be found: WEL-1

UNIT ERROR REPORT:

  1. Error occurred while reading file `'trans_1.ssm'`

To Reproduce
tide_0.095_meter_parallel (1).zip

Run the jupyterscript for the seawater intrusion model.

Screenshots
The generated SSM files looks as.

Desktop :

• OS: Windows
• flopy version 3.9.2

[jlarsen-usgs]

PR #2465 includes updates for SSM package remapping which fixes this issue.