You might want to try the 20.1.446 release. Similar to SQL strange behaviour with a begin + loop + create or replace @inmemorystorage the evaluation of sqlrowcount was not always the most current one. This has been improved in 20.1.446. Taken from https://releasenotes.invantive.com/BETA/invantive-sql.html:
Version 20.1.446-BETA, released 2021-06-11.
Enhancements:
- Differentiate error codes of Teamleader API.
Bug fixes:
- Fix sqlrowcount not set on update from within PSQL.