I have two iPhone XR and both from time to time say no sim

[XCookieX]

So in the past 3-6 months I occasionally get the no sim showing. The phone has been on and worked ok. Then suddenly no sim appears. 
I take  sims out. Sometimes it works straight away. But other times it takes awhile to be back to normal. 
also the network has been poor, worse than it was when I first had my phone( at my home anyway)  signal is great most of the time when out and about. 
I also have noticed it gets too warm when on charge. Never had this before! 
This goes for both of the phones. 

do I need replacement sims ?

[caesarome]

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@XCookieX wrote:

do I need replacement sims ?

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You could try a replacement to see what happens.

[XCookieX]

Just strange both phones do it, several times a day.