Possibilities are the liner was installed poorly and as the grout and sealants used start to break down over time, where the liner would prevent swelling of the wood and waterproof things if installed correctly, it is not doing this, leading to further issues such as swelling.
Plug the drain hole and let the shower pan fill up with a decent amount of water. See if there is water leaking from that corner that you say water appears in after a shower. If so, you may have issues with the integrity of the liner underneath. In that case, it's probably caused the wood underneath to swell. This would explain the cracked tiles and the trim separation. If this is indeed the case, you may need to get the pan rebuilt completely.
If you wish to approach the contractor following this test, I would just be reasonable, ask if they can take a look because you've noticed some leakage and unexplained damage to tiles, and see what they say after looking at it. If they suggest the liner is bad then I would ask them to do the work again at materials cost only as it is a flaw in their workmanship and two years is certainly not an acceptable lifespan for a tiled shower in my opinion. If they don't suggest the liner to be an issue (and you have identified leakage) I would get a second opinion from another reputable tradesman and make a decision on how to move forward based of the information you've been given.
If you can confirm an issue that is due to poor workmanship I would calmly approach the original contractor with this information and see what they say, if they chose to not face the issue or basically try to lie about it and tell you you need a load of work doing and they're going to charge you for it (effectively having to pay for the job twice) I would approach whatever your equivalent of trading standards is.
I may seem like im getting too far into it without actually knowing the cause with absolute certainty however, I've dealt with a lot of tradesmen who did shoddy work and lied and charged extortion to members of my family etc and want to just make sure you are prepared for whatever the outcome might be.
I hope the issue is merely something superficial.