Bose Soundlink III drops connection after connecting
I have recently purchased a Bose Soundlink III speaker (Model 414255).
I've bought it second hand, but it is in brand new condition, the original owner has not used it more than twice.
So my problem is, that when I start playing music on my iMac 2019 it automatically starts playing on the speaker, however, after like 10 seconds the connection drops and the speaker's Bluetooth sign starts blinking and it shows "not connected" on my iMac. I need to reconnect on the iMac, then it works perfectly.
Could you tell me what should do as it is very annoying and this is not the quality I'd expect from a company like Bose?
I've done the reset processes (both).
Thanks in advance