...injury during the hiatus

https://tvline.com/2018/10/31/flash-season-5-spoilers-jesse-martin-medical-leave-joe-west-absence/

Viewers had noticed that Martin had been sitting down in his scenes, or leaning in a doorway. "We wish him a full and speedy recovery and look forward to his return as Detective Joe West," a studio rep for The CW series tells TVLine.

Jesse L. Martin Set to Return to "The Flash"
by Matt Webb Mitovich
January 11, 2019


"The Flash" fans will be seeing Detective Joe West again later this winter, now that original cast member Jesse L. Martin has returned from medical leave.

TVLine has learned that Martin — who last appeared in Episode 4 of The CW hit’s fifth season — is back on set filming and will next be seen in Episode 15.




Until Joe is seen again, showrunner Todd Helbing tells TVLine that viewers will get an on-screen accounting for Martin’s ongoing absence.

“There’s an explanation, and then there’s another sort of thing down the line that will give more explanation as to why Joe was gone for so long,” Helbing shared.




It sounds, though, like Iris’ father won’t be completely MIA from these next five episodes…?

“I’ll just say there’s some technology that S.T.A.R. Labs has via which he’s gone and he’s not gone at the same time,” the EP said, cryptically.

https://tvline.com/2019/01/11/flash-season-5-jesse-l-martin-returns-joe-west-episode-15/