Thanks all for Inputs
I searched Google and found this note from Google which may happen post server migration
https://support.google.com/webmasters/answer/6033412?hl=en&ref_topic=6033383
A note about Googlebot’s crawl rate
It’s normal to see a temporary drop in Googlebot’s crawl rate immediately after the launch, followed by a steady increase over the next few weeks, potentially to rates that may be higher than from before the move.
This fluctuation occurs because we determine crawl rate for a site based on many signals, and these signals change when your hosting changes. As long as Googlebot does not encounter any serious problems or slowdowns when accessing your new serving infrastructure, it will try to crawl your site as fast as necessary and possible.
Add on Thompson Paul - Appreciate - yes its a good suggestion, will see to include sitemap