Interpolation between f09 and ne30 grids fails equilibrium checks

### Brief summary of bug

In two development cases I've set `use_init_interp = .true.` and done pSASU runs that switched between f09 and ne30 initial conditions. In both cases the SpinupStability check fails with >30% of grds showing soil C remains out of balance after > 160 years of pSASU spinup.

### General bug information

**CTSM version you are using:** [output of `git describe`]
- alpha-ctsm5.4.CMIP7.08.ctsm5.3.068 as well as
- ctsm5.3.041

**Does this bug cause significantly incorrect results in the model's science?** [Yes / No]
Yes, it makes me think we shouldn't swap between structured and unstructured grids under the current settings.

It also means I can't take PTO until 2027, which won't be good for anyone.

**Configurations affected:** [Fill this in if known.]
Interpolating between initial conditions from simulations done on different grids (here f09 and ne30).

### Details of bug
_f09 -> ne30 fails equilibrium test:_
- In [LMWG_dev#102](https://github.com/NCAR/lmwg_dev/issues/102) I started an ne30 simulation using _pSASU_ initial conditions from the end of the f09 case in [LMWG_dev#100](https://github.com/NCAR/lmwg_dev/issues/100). After 160 years of pSASU in the ne30 case both veg and soil C were out of equilibrium and 48.90% of the land surface was NOT in equilibrium

_ne30 -> f09 fails equilibrium test:_
- In [LMWG_dev#117](https://github.com/NCAR/lmwg_dev/issues/117) I started an f09 simulation using _SASU_ initial conditions from the end of the ne30 case in [LMWG_dev#116](https://github.com/NCAR/lmwg_dev/issues/116). After 240 years of pSASU in the f09 case soil C were out of equilibrium and 32% of the land surface was NOT in equilibrium (VegC was stable after 81 years)

### Important details of your setup / configuration so we can reproduce the bug

The corresponding pSASU cases in 100 and 116 that did not change grids were in equilibrium after 160 years of pSASU.

### Important output or errors that show the problem

see also
```
/glade/u/home/wwieder/CTSM/tools/contrib/ctsm53041_54surfdata_ne30_102_pSASU_Spinup.ps
/glade/u/home/wwieder/CTSM/tools/contrib/ctsm5.4_5.3.068_PPEcal115f09_117_pSASU_Spinup.ps
```