Online Streaming feature Sucks.
It takes too much time to load any web video for streaming. And if I do rewind then sometimes that following video totally stops to streaming & sometimes takes even more times to play. Totally Annoying.
And while audio streaming, there has no way to rewind forward or backward play.
Everything Sucks.

I'm facing same problem.
I tried to sync my Speed Dials & Bookmarks by signing in my Opera Account from Opera Mini's setting. After logging in I go to https://sync.opera.com and saw that nothing was synced at all. While I have more than 10 Speed Dials, 5 Bookmarks on my device but at the Opera Sync service I found nothing.
Currently using; Opera Mini 37.4.2254.133967 on Android 6.1
Using both WiFi & 3G network connection and this problem remains whatever mode I'm on Opera Mini.
Please, fix this ASAP

Now a days I've got another problem. With Automatic & Extreme mode; In Facebook when I click anything, any profile or any button, I frequently got
"Sorry, something went wrong.
We are working on it and we'll get it fixed as soon as we can.
« Back to Home
Facebook 2018 · Help"

This happens when Opera Servers got updated to version 4.123 & still on 4.125.31 this problem still remains.

And I'm totally dissatisfied with Opera Mini's media streaming feature. It sucks miserably.

Still there has problems. Opera Mini takes too much time to load any video for video streaming and if I do rewind that following video it takes another hell lot of time.
And while play/stream audio file, we can not rewind the playback forward or backward.
In Extreme mode, Sometimes facebook images doesn't loaded. If I do refresh the page then those image will loaded. Sometimes File downloading speed got super slow & if the download got interrupted then most of the times resume doesn't work.
And the full screen ads. When I'm in the middle of an important work then Suddenly a annoying full screen ad just comes up & makes me crazy.

No Way.
Opera Mini developers set this full screen ads like this. No option to opt out from this. But maybe there is a way. Disable the ad module using 'Lucky Patcher' app.

I enabled "Keyboard Suggestion" & "Hardware keyboard Suggestion" option from the settings menu of Windows 10 v1803. While Firefox & Chrome browser can show keyword suggestion Opera can't. Please, fix this ASAP

Nope, man. It's not fixed yet.
Check it again.
Check the full Wiki page of Opera Mini. And then you'll find out.
I've two devices. Samsung Galaxy J7 & Motorola G5 Plus. My friend has Xiaomi Redmi 4X. Facing this problem all of those devices. Both in Automatic & Extreme Mode.
So, check it again & fix this ASAP.

Huh, this will never be fixed.

I alredy filled bug report for this problem but developers seems careless. And I've to write it again. Please, fix this ASAP.
On some websites Opera Mini can't able to render font as well. Texts are overlapping each other & can't able to read only in Automatic / Extreme mode.
I browse Opera Mini's Wikipedia page https://en.wikipedia.org/wiki/Opera_Mini
& saw this problem :