Bose Soundtouch app sometimes can't locate the speaker

I have a Bose Soundtouch Series III speaker system which connects to my new iPad mini 4 most of the time. But every so often, especially when I return to the Soundtouch app after doing something else on the iPad -- in order to raise/lower volume, change stations, etc. -- I get a message "Hmmm...Soundtouch can't locate your speaker". Sometimes I can just click the link "Speaker is already on network" and it will connect. And sometimes I have to force the app to close and it will then connect with the speaker after I restart it. Other times I have to go through the whole reconnecting procedure on the speaker (holding the "2" and "-" buttons to enter the speaker's setup routine).

I've reinstalled the app on the iPad, and I have the latest OS (11.2.1, I think) as well as the latest updates from Bose for the speaker. And -- strangely -- the Bose Soundtouch app on my Android phone never has this problem. Everything else on the Bose works beautifully -- I get an excellent Bluetooth connection from iPad to the speaker (something that isn't always true with my phone) and all the Wifi and internet radio functions of the speaker are problem-free, as long as the iPad Soundtouch app doesn't crap out. So is this a Bose problem, or an iPad problem?