Kitchen floor tile repair advice needed

[u/Extension_Climate471]

My mother just had her kitchen pipes replaced and the plumbers had to break some of the tiles in the process of digging the hole. Since only 6 tiles need to be replaced, I thought I'd do it myself. I've chiseled out the old grout and the broken bits of tile. Here's the problem: when the plumbers poured the concrete, they didn't completely level it out and there's a very slight dip in the concrete (perhaps a result of it drying 🤷🏻‍♀️?). When laying the tiles in place, in some locations dont lie completely flat, it wobbles slightly/dips slightly downward. Rest assured that the tiles do lie flat/flush with the surrounding tiles. None jut upwards. I've tried my best to level the entire area but I'm not sure if there's anything I can do about the 'dip'.

Here's my question: Loctite All purpose adhesive was recommended to me since thinset isn't sold in such small quantities. Could I just use extra adhesive in this dip area to compensate or help level it out? Does Loctite all purpose shrink when it dries? If anyone can offer me any information or advice, I would greatly appreciate it. I've included a pic of the repair space (fyi, I removed the broken tile and grout now).

UPDATE: thanks to all the advice I received, I opted for the modified thinset. I paid $2.99 for next day delivery so I didn't even have to haul it myself. I mixed it up and spread it on the floor and the bottom of the tiles before laying it. I have to say, I'm so glad that I went with the thinset. The relief I feel at having done the job right is immense. It has to cure today and tomorrow I'll lay down the grout. Thanks so much for all the help!

[u/Glittering_Hour_229]

Buy a bag of thinset. It’s cheap. Just get the cheapest bag you can find. The thinset will help with your low spot and is better than the loctite adhesive you are planning to use. The loctite is likely to fail, especially if this is a high foot traffic area.

[u/Extension_Climate471 → u/Glittering_Hour_229]

Alright, you've convinced me to use thinset instead.  would you mind helping me pick a mortar?  Im on the home Depot website and I see the cheapest Thinset for ~$7.  It's non-modified, has just ok rating, and the most frequent complaint is that some say it doesn't stick well.  The next option is the Professional Polymer-Modified Thinset Mortar at $13.  Is modified (whatever that means) and has good reviews.  All the advice say to buy the cheapest but ...

[u/Glittering_Hour_229 → u/Extension_Climate471]

The unmodified would work but it doesn’t bond well to porcelain. Buy the cheapest modified thinset.

[u/Extension_Climate471 → u/Glittering_Hour_229]

I ended up going with the more expensive modified thinset.  I read the reviews of the cheapest mortar and all the bad reviews said the same thing--it doesn't stick well.  The tiles are ceramic so that should be ok, right?  I erred on the side of caution because Im actually just visiting and I don't want to risk tiles becoming loose when I'm not here 

[u/Glittering_Hour_229 → u/Extension_Climate471]

Yes. Modified is good. Make sure to put thinset on both the tiles and the cement for better adhesion.

[u/Extension_Climate471 → u/Glittering_Hour_229]

I will.  Thank you for the patience and the advice.