Two PPPoE from the same ISP is no problem, the restriction on shared gateway IPs is only applicable to Ethernet, not PPPoE.
Guessing you probably don't have any config in place to load balance traffic, what does your config look like? Config info here.
https://help.ubnt.com/hc/en-us/articles/205145990-EdgeMAX-Dual-WAN-Load-Balance-Feature