Time Machine progress bar gets stuck

[Mac2013orlater]

Time Machine on OXS X 10.9.5 to sparse bundle on LAN.
While doing the backup and when the progress bar is at the point of approx 80% it gets stuck
for more minutes (3 to 5 minutes). In other regions the bar makes, even if slightly, small but clear visible
progress steps. Is this a known phenomenon? What are possible reasons? How to fix?
"Verify backup" is made prior to every backup run and follows such.
Compacting the sparse bundle was made recently too. No help.

 

[Mac2013orlater]

I missed to add some details which might be significant to have whole picture of the situation.
* Verify and Do Backup are affected
* As soon as the got-stuck stage ends (as said its duration can be up to 5 minutes)
the backup continues and completes successfully. No other probs observed than those
get-stucks. The delay in having backup process completed is irritating, therefore this thread was started.