It happened due to the several facts problems: -
When server stopped responding
Your Internet connection has problems
You manually pause it
Stopped it to download it later sometimes. While you know it has the capability of resuming.
IDM failed, when it send the request to download it where it has stopped.
Response of the IDM was "ed you want to download it from the beginning. Definitely you don't want to download it from the beginning while you have downloaded 1 GB or more. There are the tips and tricks to download the file from where IDM has stopped or you had paused it.
Open the same file in the browser, click to download it again, when dialogue window appear select to download it later
(Check to ensure that the file must have the same file size and from the same link/server).
Open IDM manager window and double click the file you have selected to download later
Select the f#ll address field and press ctrl+c to copy to the clipboard.
Now, double click the file which has not been resuming and paste the address there which you have copied earlier in the address field press ok.
In the IDM manager window click the file and press resume. 90% of the resuming problems has been resolved by this little tip and trick