Thank you all for your precious inputs!
Jaxx Liiberty is available for iOS and Android, but there are also desktop versions for Windows and Linux. GazetaBitcoin never mentioned which one he uses unless I am wrong about that.
This is true, I forgot to mention that. I am using Android version.
I tried testing Jaxx wallet few years ago and I dropped it soon after.
This wallet is full of bugs and I heard many complains from other people, so I wouldn't risk using it and I consider it a waste of time.
If you have private keys or seed words use them and import them in different open source wallet that actually works.
If you need some multi-currency supported alternative mobile wallet that is open source, consider trying Atomicdex or Unstoppable wallet
Thank you for your suggestion, dkbit. The other wallet app I'm using is Bitcoin Wallet for Android. I will give a try to the ones you mentioned. About Jaxx, you are right. However, what I found interesting about it is the fact that it contains 2 anonymous exchanges inside it, allowing you to change a cryptocurrency for another one without offering personal information.
You also can try to clear the app cache or reinstall Jaxx completely, but if there is a bug in the wallet's codebase itself, you can't do much about it.
If you have the seed and/or private keys, there shouldn't be problems with wallet recovery. [...]
you can then clear the cache or re-add your Bitcoin wallets on Jaxx.
Thank you for your thoughts as well, Pmalek and witcher_sense!
In the end, I managed to solve the issue. At first, I checked all the articles posted by witcher_sense, but they were years old and they were not addressing my problem. First link was about missing funds, the second was about missing funds after upgrading from Jaxx Classic to Jaxx Liberty, third one was suggesting to make the upgrade (which I did many months ago) + use app's refresh function (which did not offer me any positive result) + clearing app's cache (which also did not help me), while the fourth article was saying about some possible problems leading to incorrect balance, but none of them was for my case. This problem (meaning to not correctly synchronize the balance) appeared only recently on Jaxx and I never had it before.
So after checking the articles I tried to clear app's cache, but nothing changed inside the wallet.
Then
I said a prayer, I uninstalled the app and reinstalled it. I used the recovery phrase and --
voila! -- my funds were shown correctly on app's main screen, in the Bitcoin wallet shown there and also in the upper part of the screen, where the cumulative amount is displayed.
Now I can see the entire amount I was supposed to have (and which I actually had, as it was only a UI error).
Thank you all again for your inputs, your observations were very valuable and now I managed to fix my problem!