WAN from DHCP (re0) to PPP (cuaU0.0) and back problem

[chol]

In OPNsense 15.1.10.1 the WAN will get reassigned from re0 to a PPP (cuaU0.0) type connection (LTE, UMTS) but afterwards not back to DHCP based on ethernet driver (re0 in my case) .
The GUI gives the warning message:
"The following input errors were detected:  You have to reassign the interface to be able to configure as dhcp."

When trying to do this, the reassignment Interfaces > (Assign) > WAN is clickable in the boxed selection to "re (mac)"  but no "save" button will appear.

The alternative reassignment cycle: DMZ (re1) to re0 and then re1 to WAN will also not function:

after clicking  Interfaces > WAN > Enable -> check Enable Interface and IPv4 Configuration Type to DHCP and "Save"
it shows the same error message as above:
"The following input errors were detected:  You have to reassign the interface to be able to configure as dhcp."



Resolve attempts:

#1: An attempt to un-assign the interface, reboot  and assign again, does not function.
#2: Destroyed the PPP connection and reassigned DHCP on re0 does not function
#3: reassigned to re0 and applyed a static IPv4 with GW did function

Resolved: After #2 + 3 did establish a DHCP config type to WAN (re0) , eventually it did function