To clarify [potentially misleading] information that you will see elsewhere in this thread.
Force-closing an App is generally unnecessary. Force-closing an App clears all system resources associated with the specific App, this sometimes being a necessary intervention to terminate a malfunctioning App. Reinitialising an App consumes slightly more power than simply resuming an already initialised App from its idle state.
Force-closing an App (or Apps) is entirely different to a forced-restart of the iPad itself. A forced-restart of the iPad re-initialises the Operating System - again, this sometimes being a necessary intervention to clear a malfunctioning system-level process (such as the issue that you describe).
A simple restart of the iPad, while releasing some resources, does not fully re-initialise the OS. A simple restart can be used to constructively clear some issues, but is not a substitute for a forced-restart.
No harm will come to your iPad in performing a forced restart or a forced-close of an App or Apps. Both of these processes are necessary in some circumstances. The only short-term impact is a temporary increase in battery utilisation while the OS or Apps is/are initialised. A forced-restart of iPad may result in loss of unsaved App-data in some circumstances, unless the App is closed prior to the restart.
In summary, Memory Management is generally a juggling act - and for the most part, you should allow the OS to manage its memory space. Re-initialising an App is the slowest and most power hungry method of launching an App. Inactive Apps do consume some system resources, but by design, the required system resources to maintain this state are insignificant. Force-closing an App releases all associated resources associated with the App. This manual intervention sometimes being necessary to terminate an App that may be malfunctioning.