Hello Mreams,
Welcome to the community!
There could be many reasons why one phone may show better (or worse) signal than another phone.
Firstly, it's not uncommon for different phone models to have differences in cellular reception. For example, a professor at Denmark's Aalborg University tested the performance of various mobile phone antennae (see here). I'm not sure how much we can extrapolate from his data because Fido/Rogers uses mostly different bands/frequencies and the study is now a few years old. However, it does illustrate the large differences between phone models.
In addition, different phones might illustrate the signal strength differently. There is no industry standard that relates cell phone signal strength to the number of bars on your phone. For example, the same signal strength (-90dBm) might be shown as 3 bars on one phone and only 2 bars on another phone. It is far better to compare the actual decibels. -50dBm is great signal or full bars. -120dBm is very poor signal or a dead zone.
Another possible reason for differing signal strengths has to do with the band or frequency to which the phone is connected. The different frequencies have varying characteristics. The higher frequencies do not travel as far, nor penetrate as well as lower frequencies (see graphic here). In addition, cellular reception is dependent on your location relative to the cellular towers and the bands/frequencies used at those towers -- not all bands/frequencies are used at all cellular towers. You can get an idea of your surrounding cellular towers here.
What version of the LG G6 do you have? For the moment, I'll assume you have the Canadian version (H873) of the phone. Surprisingly, that version does not appear to have all of the compatible bands/frequencies (see here; and here for compatible bands/frequencies). (The Canadian version Samsung Galaxy S8 does have all of the compatible bands/frequencies; see here). It's possible that your S8 is connecting to band 7 at a closer cellular tower, whereas the LG G6 can only connect to band 12 from a farther cellular tower.
Since both of your LG G6s show the same signal strength in your area, it's likely a function of the phone model version and your location rather than a faulty G6. In addition, the fact your phone can get better signal at different locations also suggests it likely has to do with the bands/frequencies to which the phone connects.
Hope this helps 
Cheers
Hey @mreams
Welcome to the community
I'm sorry to learn you're having issues with your LG G6. Just to clarify, does this happen everywhere or only in a specific area? Also, do you ever get more than 2 bars on LTE on this phone?
Let us know!
