Turbotax is a self-prepared return. so if the direct deposit info is wrong then either YOU entered the incorrect bank info or you elected to have Turbotax fees taken out of your refund. in that case the refund goes to a third-party bank where the refund is split between the fees and the balance of your refund. the third-party bank then electronically transfers the rest to the direct deposit a/c you specified. if it is invalid, then the receiving bank sends it back to the IRS so it can mail you a paper check.
none of this has to do with a refund lower than expected except possibly for the fees taken out. most reduced refunds are due to claiming the stimulus credits again when the IRS records show you already got it. there can be a myriad of other reasons. if your return has been processed you can go online to review your tax return transcript to see what the IRS changed.
https://www.irs.gov/individuals/get-transcript
in any event, if the IRS changed your return, they will send you an explanation so you can refute the change. this can take many weeks.
