TMSL refresh not completing whereas manual refresh in SSMS completes

Question

We have a fairly large AAS tabular model and the largest fact table is partitioned by month (returns somewhere around 200M records by end of the month. When we process a partition manually through SSMS the "full" process completes in 2-3 hours. When doing the exact same thing through a TMSL script (run from ADF or even on the server) it continuously spins and never completes. The source is CSV files in data lake storage (ADLS Gen2).

We can monitor the AAS resource from Azure portal and can see it is active (reads, thread usage) for about 3 hours and then nothing, but the TMSL script won't complete and seemingly data will get read but not saved into the partition. Even empty partitions (no data) for this table take ages to process from TMSL.

We've tinkered with server settings and timeouts are all set fairly high. Any explanations as to why refreshing via SSMS is proving different results than executing via a TMSL script.