Azure APIM ETimedout error intermittently

I have two APIM(BFF and Enterprise). Both has azure functions as their backend. The azure functions are running on premium EP1 plan and has two instances running all the time.

BFF APIM receives call from an ios application and routes its call to a nest js graphql server. The nest js server is running as azure function. The function calls enterprise APIM. The enterprise APIM has its own .net core based azure function.

In the BFF nest js GQl server, we have a middleware function which makes a call to the Enterprise APIM before running the 'real' query. We started to receive 'Etimedout' error in last two weeks. But the error has really picked up in last couple of days and it has rendered the API unusable. The error typically says ETimeout error on the enterprise APIM 443.

I already check the SNAT. Also, scaled up the max burst instances of azure function to no avail. Nothing has changes in terms of load of the system. It has been consistent throughout last 8 weeks. Any ideas what we can do from diagnosing perspective?