Hmmm … both things shouldn’t happen.
Did you confirm the slot was actually changed back?
Does fastboot getvar current-slot still give back a or b now, or something else?
fastboot getvar current-slot gives back current-slot: a
When I change to b then it gives back b. After reboot I get that error. Then I choose ‘Try again’ and hold the Volume down-butto to get into fastboot-mode again. Then the getvar still says b. I change nothing and just tap ‘Try again’. After the third time the phone boots into slot a again, where is the buggy OS.
But the buggy OS boots?
I’m having the exact same problem. My active slot was b, I changed it to a and then when I reboot I’ve got a message saying my data may be corrupt.
So I changed it back to b, now I can reboot but I cannot call 
My telecom provider is Orange France
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Since this procedure worked for users in the past and this error doesn’t make much sense as the update seems to have worked (only that the OS is buggy) and there was no up- or downgrade of the major Android version … it seems I’m missing something. Sorry.
I edited my earlier post.
This really is a neat feature of A/B devices … if it works. Bummer.
Yes, it does.
And my provider is Vodafone Germany.
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I also tried using other dialer apps and same issue. Not even working with apps like Signal, Whatsapp or Facebook
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Hi,
Same problem here with my FP3 with both my SIMs, one from Orange and the other from SFR.
Doesn’t look like it’s related to the carrier.
Doesn’t work with another dialer either…
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Ah, I misunderstood then. I thought you got the factory reset offer on both slots now, which I wouldn’t have understood at all. Phew, world view intact.
First it looked like that it wouldn’t reboot neither from slot a nor from slot b but I was mistaken. It boots from slot a (0.18) but not from slot b anymore.
What about the others facing the dialer-problem? Can you change the slot and boot into the old OS?
I can change the slot but I cannot boot into the old OS
Yes, that’s what it looks like in v0.18 on my Sony XA2 too. (nothing to do with ballet) 
Here’s some weird behaviour, somewhat related, on Sony XA2 running v0.18q and using the default phone app.
Could not make calls. Every number dialled would fail immediately. I made small adjustments to the apn settings to correspond with what they were on android 9 (that’s the last stock for this phone) and tried again. Nope. Restarting the phone in between any changes. Tried calling the phone and it always got the busy message.
Put this sim into another phone: no problem, all normal.
Put another sim into the xa2, same carrier: no problem. Strange. But at least all the sims and phones are working.
Moral of the story: witchcraft and magic involved sometimes.
BTW the sims are PAYG from 3 in the UK. One of only two surviving strictly PAYG options left…
Also a known issue :
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Somewhat replying to myself here: Just had a phone call (I got called) that worked all fine. I activated the loudspeaker mode immediately (wet gloves ) and the other side only complained about a slight echo of herself. O2/Telefonica Germany.
Hi,
I installed the last update of /e/ on my Fairphone 3 two days ago and since then phone calls don’t have sound.
Neither I or the person I call can hear something. This also happen if I try to call with Signal, Whatsapp or Facebook.
I also tried to call using different dialer apps but with same result.
I know the speaker is still working because I can listen to my vocal messages.
I tried to restart my phone many times but still the same.
Does anyone facing the same issue ?
Thanks
Regain your privacy! Adopt /e/ the unGoogled mobile OS and online services
You could answer yourself if you had read only one screen page of the forum.
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Thanks !! I missed that
I’ve just updated this morning my FP3 to /e/OS 0.18-20210813129945 which I received via OTA.
Not sure it’s the right place for that, but if needed I can create a new thread.
All was running just fine with last /e/OS 17 branch version installed.
All went well after upgrade, until I received a phone call. I was not able to hear the person as I was not able to use the mic as well. 
Originally I thought that it was coming from the MIC driver itself or so…
When I use signal app for phone call I have the same issue.
But I can record my voice and send it to signal as a message.
I’ve tried with a bluetouth headset and no luck as well, I can hear the person but no sound is received by the person.
So I suspect an issue at the sound manager itself and not driver level, since I can listen some sounds and record sounds in some conditions.
I’ve tried to reboot, but no improvement. My phone is fully charged.
Any idea what I can do to get that fixed ?
As you can understand, as the basic function of a phone is broken, I will not be able to stay in this situation. So if some logs needs to be collected let me know very soon.
I plan to do a factory reset maybe tomorrow or the day after to give a try, but I’m very reluctant to do that as I will have to reinstall evry thing