For me it is repeatable. Steps are as follows:
Turn on the phone with 4g enabled. 4g+ initially works, but if I look after 10-15 minutes, the 4G+ symbol is gone. If you use an app which requires an internet connection, it will show “offline”.
It can also be repeated using the following steps:
Phone in 4G+ mode. Turn on wifi. Let wifi connect. Wait for 30 seconds. Turn wifi off. At this point 4g+ reconnects for a short time, and then drops the connection and goes offline. For me this is repeatable every time.