Samsung S21 5g sim slot 1 problem

[Capman]

I was using my smarty sim in slot 1 since had the phone no issues full 5g signal but the past couple days my signal has dropped down to 1 bar on H+ its only doing it with smarty and 3 network on slot 1 any other network is working fine but when i put my smarty sim in slot 2 its works perfect full 5g signal again so why is slot 1 now not working with my sim it was perfectly fine for months 

[BandOfBrothers]

That is a conundrum @Capman 

I personally do find my o2 sim card work better in Sim Slot ² and my ee sim card works better in Sim Slot ¹

No idea why 🤔

I'm OK with this on my phone however if you wish you could try the following troubleshooting steps. 

> Clear Cache Files from the phone's System Partition Section  > https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/ You may need to insert your earphones or hook upto a powered On Laptop or use a Tv's USB Port to access the Clear Partition Section. This may help with lag or stutters as this clears the phone of old/unused or broken cache files.There is also a Repair Apps option in the Menu System too. 

> Diagnostic Tool found in your Samsung Members App. 

> A Samsung Service Centre can take a look. 

If I can be of any further help then please don't hesitate. Take care.  😎