Maybe the play store (the download service) got force closed due low-ram then got restarted back when the phone has more free ram. It happened with me too, sometimes, cant complaint though, as the job still be done.
And if you feel some apps feel heavy/lag, maybe try other alternative apps (like i use naked browser instead of chrome). If you dont find the alternative apps, maybe it's time to realize that you need newer (and more powerful) phone.
And for the dude who want to install cwm: why do you want to install cwm? Do you have specific reasons to must have cwm? Maybe you can flash cwm into the fota partition just like twrp (havent tried it). But i dont think there is advantage to have cwm than twrp, if you have problem flash naosp rom (in mine it has error when flashing naosp rom in twrp) you can flash doomkernel first (it has cwm built in the kernel and it will bypass the recovery in fota partition)