A TRV is a TRV. It doesn't matter if it says visitor, student or worker; all that matters is that it is valid. There is no link to the IRCC website stating this, just as there is no link stating that people need to apply for a new TRV when their status changes.
Tell the person in the Whatsapp group to quote IRPA or even the IRCC website to support their claim. They won't be able to because they are wrong.
Aside from that, a person applying for inland sponsorship should not leave Canada for 4 weeks mid process.