Cat I am sitting has not been seen for five days

[Sonolanona]

I'm a cat sitter and having the worst week ever.
I love cats, I have cats and my job is cats.
And for the first time one of my clients has gone missing :(
He's an indoor/outdoor cat with catflap microchip and lives in a rural location (think orchards,stables etc) and I have not seen him for 5 days. His brother is there every time I visit (twice a day) . I have varied the visit times and even gone back three times in the evening but no sign.
The owners are away for several weeks.
I've called all the vets and no cat of his descritption has been brought in, which is good but I'm so worried and sad... I've never had a cat go missing on me before.
All the food is being eaten so maybe he's just coming in when I'm not there, but if I can have some cat returning vibes please...

return it once you've used it ?!

Just do the camera. Far easier than searching huge areas.

Just to reassure you we have a.microchip cat flap (but one that send notifications when he leaves or returns) and a ring doorbell, when we go away without fail as soon as I get a ring doorbell notification to say the cat sitter has arrived I get one from the cat flap to say the cat has left. We went away for two weeks and the sitter saw our cat once through a window

Any news, OP?

No news but I've messaged the owner to ask if I can put a little camera in the utility room where the food is... I might find it useful for other pet sits so will buy one.
Still no sign of him :(
Had a truly rotten start to the day... on my way to see to the cats I spotted something at the roadside...wasn't sure if it was a rabbit or cat. Did my duties and on my return I pulled over and it was a beautiful fluffy ginger boy, clearly dead but still warm. I couldn't leave him in the rain so lifted him into my car to take to the nearest vets. As there are only a few houses, I pulled into the nearest driveway just to knock and a lady was just leaving for the school run. It was her cat 😢
Her husband came with a towel to lift him so the kids didn't have to see him (very bloody) but it was awful. At least they know but having lost cats myself I know how devasted they feel.

Oh OP what a tough old time you are having.

I think the camera is the best idea. Good luck.

Camera installed (with owners permission of course) but sadly overnight only the not missing cat was in and out. The camera is great and I will probably find it useful for other clients if their owners are happy for it to be set up. Some of the other houses I go to already have them and I never mind being on camera as they can see I'm doing my job!
This evening I am going to knock on the doors of the neighbours (not really neighbours as the homes are quite far apart) that I havent spoken to, and ask them to check outbuildings just in case. Unfortunately a lot of the area is farmland and the sort of places a cat could easily get locked in barns or tractor sheds. It doesn't help that he wasn't very well when they went away (had a cat cold..had been checked by the vets but was snotty) and I do wonder if he was more poorly than they thought :(
I'm doing everything I can, but it just feels awful..I have never had a client's cat go missing before, but have lost one of my own years ago and it's just miserable.

I'm sorry OP this must be so stressful for you. Have you left the camera there? Just thinking of the live in a large rural area it's perfectly possible that the 'missing' cat may return for food more sporadically?

What's the owners take on this? Are they worried? Is the cat nervous or often go away for long periods of time?