Venu 2 plus disconnects

There are several issues with Huawei and the Venu 2 Plus.
My Vivoactive 3 worked well for years, independent of restarting, flightmode or disconnects. But it has not this "fancy" 6-digit code on every reconnect.
My painful journy can be read here. I´ve replaced the phone now...

No, it's not supposed to work that way. You should only get that code prompt once. Could be, as HerrR mentioned, a problem with Garmin and Huawei. 

You can try forgetting the phone from your phone's Bluetooth connections, then re-pair it. 

Yup, as I mentioned in the linked thread:

The watch constantly checks for the phone. If it´s there it connects.
If not, it goes on searching.

But if the watch found the phone and the Connect Mobile Service is not (yet) started, it fails and prompt the PIN exchange.
Due to the Huawei way of killing services, the Connect Mobile App must run and be removed from the battery optimizer.

So restarting the phone and/or killing the Connect Mobile App or the Service behind, will force the watch to reinitialize the BT low energy connection. Which sometimes will interrupt the phone, because it "thinks" its already connected.
On my Honor 10 it was even a much bigger mess!

From my point of view, this can only be solved by garmin. If the watch finds the phone, it seems to initiate the connection with Connect. If this fails, it should just keep on trying and not offering a new pin.
On my Google Pixel I also have to enter the PIN after restarting the Phone.

Thanks for the answers! I guess this sucks. Really annyoing. 

Then I may have to return the watch, even though I like it. But reconnecting everyday seems like a struggle... 

It could be related to aggressive power management on EMUI.

I don't own Huawei phone, but once I disabled PowerGenie on my friend's phone, all his problems related to apps background functionality (for example emails not delivered to the Outlook, no messages delivered to the Signal, no SMS delivered in case of chat features enabled, ....) were fixed.

Give it a try (you can enable PowerGenie later and bring all its functionality back) 

 How to disable PowerGenie

Try this https://forums.garmin.com/apps-software/mobile-apps-web/f/garmin-connect-mobile-andriod/283174/repeated-bluetooth-pairing-codes-after-disconnecting-watch/1428040#1428040

Sadly you are not the only one and is not only on Huawei phones. I have a Mate 20 Pro, and the solution above worked for me.

I have the same phone and no issue with my Fenix 6s Pro, not sure whether the Venu 2 Plus is more critical in this respect, as other already mentioned make sure that battery optimization for the app connect is disabled in case non already done:

Settings>battery>app launch>find the Connect app and disable manage automatically, make sure that all 3 sub menu options are enabled. For me it is already enough this way, eventually to make sure also open the app Connect, tap on the square botton and look for the Connect app floating window, pull down the window and hold it a while until the small locker appears in the upright corner as sign that app is always kept running. 

when in the morning you turn off the phone inflight mode if not connecting automatically just open the connect app and click on the device icon to sync the device. Hope it helps.

I get the exact same thing with a Google Pixel 5. Once connected I have to add the watch to the Garmin Connect app all over again each time too.