Recently, we've been seeing HTTP "wrong status line" errors when hitting the Leads REST API endpoint. The status line is an expected line in HTTP responses (see section 6.1) that "[consists] of the protocol version followed by a numeric status code..." and looks something like this "HTTP/1.1 200 OK". Effectively, this is just the part of the "header" for an HTTP request. However we're seeing the error wrong status line \"<html>\".
Based on this response, we're guessing one of two things:
1. The expected response content is supposed to be JSON, but this is obviously HTML. This could mean that there's a maintenance HTML page put up instead of a specific "maintenance" JSON response. This usually shouldn't affect the HTTP response headers... but depending on how the configuration is set up for putting up this maintenance page, it could. Additionally supporting this "maintenance" page problem is that these errors happen almost universally around 04:34 UTC (which is 23:34 EST).
2. Potentially, there's a problem with the request we are sending, and the returned response doesn't handle it properly. This seems unlikely as we can see the raw request we are making and it is in line with the Docs for the Marketo Leads endpoint. Also, while the error occurs often, it is still intermittent. This means that its less likely that the request itself is the problem (but not impossible).
If we could have some Marketo developer attention into this issue that would be most welcome. Even if the problem is just maintenance, it will give us an answer and a course of action to resolve these issues.