Regulators are probing Comerica after a botched technology upgrade left the bank’s wealth-management unit short millions of dollars.

The Office of the Comptroller of the Currency has been looking into a wealth management platform change at the bank that led to widespread errors on transactions for trust clients, according to people familiar with the matter and internal emails reviewed by The Wall Street Journal. Executives at the Texas-based bank told staff the errors could force them to potentially write down any funds they weren’t able to chase down.