This problem is rather old and needs to be fixed, we all have it AFAIK. You can change the source from phone to system or somesuch, but then the reverse happens. Also it's odd when speaker is used.

However, the app is quite promising and I'm sticking to it as long as someone keeps developing it.

ETA:

Now that I reviewed my call log (didn't do that in a while), I noticed why it's so dang slow. No wonder, seeing as it records everything twice. First time when an incoming call happens, then again with the notification. The second call is a few seconds behind.

I think maybe it's because I have both icons on desktop? Also, one is system recorded, the second is Phone or something like it because one is clear and the other has ambient sounds and clicks on it. Also, one has a lower volume for one party.