iPhone 6s GPS disconnection with 4G+ LTE 1800Mhz

It seems more and more likely that new Iphone 6s have a GPS problem when the sim card connects the Iphone 6s on a 4G+ LTE with the 1800Mhz frequency.

Here in France, Bouygues Telecom provides LTE at this unique frequency 1800Mhz and any Iphone 6s have this problem: after 20 minutes or so, Waze or whatever Map using the GPS, will disconnect and outputs a random place. The boussole itself is getting fool. The unique solution is to force the Iphone 6s on 3G to get the GPS back.

- Other French operators will have access to 1800Mhz in January. Iphone 6s using an Orange or Free sim card, which are currently connected to other frequency of the LTE, are working well.

-Other smartphones, like the Iphone 6, connected to the same Bouygues 1800 Mhz LTE are working well.

Without any information neither from Bouygues (http://forum.bouyguestelecom.fr/question...) nor from Apple (https://discussions.apple.com/thread/729...) since about a month now, I suspect a strong hardware problem which probably won't be solved by software and I would like to know if someone got this problem in another country and if a technician could have information on the interaction of the 1800Mhz with the GPS.