This is an unfortunate recurrence.
Met statement: Jonas Kaufmann has canceled his performances in this season’s new production of Puccini’s Manon Lescaut due to illness. Star tenor Roberto Alagna, currently at the Met giving an acclaimed performance of Canio in Pagliacci, will sing his first-ever performances of des Grieux in Manon Lescaut, replacing Kaufmann. To allow time for him learn the staging before the February 12 new production premiere, Alagna must withdraw from his remaining performances as Canio as he undertakes this new challenge.
Kaufmann cancelled Carmen at the Met last year. Recently he gave acute sinusitis as the cause for pulling out of the Real in Madrid.
Some more detail here.