The mobile version of Housing leads conversion has dropped by 3% over the past 2 weeks. How would you analyze the reduction?

Housing is a portal that allows users to buy, sell and rent properties in India.

Question-
The mobile lead conversion rate dropped by 3% in two weeks. 
Try to understand from the interviewer the metric for calculation 
Lead conv. rate = Total no of clicks on contact seller  / Total visitors 

Is it the total number of visits or unique visits - Total visits 
Is it on mobile website, android app, and IOS app - Yes
Any other platform that is counted - No 

How did we calculate the drop?
Compared to today's lead conversion rate wrt two weeks ago -No
Compared the current bi-weekly lead conversion rate to the normal existing rate - Yes

Is this for any particular business? - This is for users who are looking to rent/buy properties.

There could be
3 broad categories of reasons 
1- Internal: Includes app updates, data changes, app performance, users/product/marketing/ device/geography segment changes
2- External: Competitor's easy process. Changes in user mindset over what was existing two weeks ago.
3- Others: Probably it's not a problem: 

The sequence of figuring out the problem 
Others --> Internal (using the user flow)--> Internal (outside the user flow)--> External 

Others 
Metric change, something go added into the metric calculation, 3rd party which is capturing this metric has errors, this is a seasonal change, this is observed across all property sites due to some events, the change is very insignificant and has been observed multiple times.
Is any of the reasons mentioned below are true - No

Internal (Using user journey)
Assuming the flow is the same for property rent and buy. I will ask the interviewer to correct me if I am missing any step or oversimplifying anything.

1- Getting users to the platform [Paid: ads, affiliates, Unpaid: Organic, social media, notifications, mails]
2-User Opens platform 
3-User selects: Property type and location [Is there anything else on the page, the interviewer says -No]
4- user clicks on a search. 
5- user views a list of results 
6- user selects a property 
7- user views property details 
8- user clicks on contact seller
9- user is asked to add mobile number if not logged in 
10- user adds a mobile number 
11- user received an OTP
12- user enter the OTP
13- Done - User is counted as converted lead (into opportunity)

I will tell the interviewer that in the metric calculation, you had confirmed that it is # click on contact seller/ # total visitors. Probably the metric should be #of users who complete step 13 / # total visitors
The interviewer says - Okay

It is a long user journey, let me first try to figure out the problem area by asking drop rate at some of the steps.
3 - # users who select location and property type / # users at step 2
4- # users click on a search/ # users at step 3
6- # users select a property / # users at step 4
8-# users click on contact seller /# users at step 6
9- # users are asked to add a mobile number if not logged in / users at step 8
10- # users add a mobile number /# users at step 9
11- # users received an OTP /# users at step 10
12- # users enter the OTP /# users at step 11

There must be a drop in one of the above numbers, tell me where?
Okay the drop is in metric 3

Okay so tell me
How many UI screens do we have between 2 and 4 - Only 1 screen
Any elements like popup or chat - No
Do we have anything apart from location selection, property type selection, and search button on the page - Okay, we assume it to be true 

Tell me if any of these are true- 
1- Any UI changes [in the last two weeks]
2-Any changes in dynamic data like text, dropdown list, etc.
3-Any App performance issue on the page like slow 
4-Any 3rd party element issues like location autoselect from mobile's location etc. 

Interviewer- No

Internal (outside the user flow)

Who are they: Hypothesis- A particular segment had a lower conversion rate and that segment visited the platform more in the last two weeks. 
Any change in new users/existing users?
Any changes in segments we have targetted in these two weeks? like bachelors, families, office properties, shops 
Any changes in the segment in terms of gender, income, and other demographic details?
Any changes in location-based segments? Like added new cities, or targeting tier 3 cities
Any change in new user vs existing user segments?
Any change in traffic in segments based on App engagement? Maybe we predominantly sent notifications to users who are less engaging and hence less search completion rate.

From Where are they coming:  A particular platform/device had a lower conversion rate and that segment visited the platform more in the last two weeks
Any change in total visitors in mobile, Android App, IOS App?
Any changes in total visitors in device with particular screen size etc.

What they were looking for: A particular type of property had a lower search rate and that segment got more visits in the last two weeks
Any changes in users who are looking to Rent property/buy property?
Any changes in the users who were looking for maybe 1BHK and other types of properties?

When are users coming: 
Is user traffic comparatively more on weekdays? 
Is user traffic more at the particular time of the day when the search completion rate is lower?
Interviewer - No

External reasons
Have users started to expect something more on the search page in the last two weeks, and they do not find it on the platform?
Is that bad marketing like if you search for a place, housing will sort of use that location for ads, etc.

Interviewer - No

Okay, that's all I could think of, do you want me to think about anything specific?