True! But that isn’t always the case. There are many instances where Historia touches Eren and nothing happens (ie. when he is chained up in the cavern in S3 and Historia punches him and calls him a ‘cry baby).

The first time Eren realises he can see ‘future memories’ when touching a Royal is in that same cavern and Rod Reiss explicitly explains the connection - essentially saying ‘here Historia, touch Eren and bc you’re royal something crazy will happen to his memories).

If he knows Historia is royal and can activate memories, that’s why he would have potentially ‘expected’ it when kissing Historia’s hand. Infact, it seems that he can only really summon his Titan powers when there is awareness or ‘will’ involved (eg, he can only use hardening when he ‘wills’ it, or when using the founding titan to ‘save Mikasa’ from Dina.)

So, if Eren and Armin aren’t aware of Armin’s heritage, it could easily slip under the radar.

And even still- the first time Eren ever has a memory of being injected with the titan serum from Grisha, he is leaning against Armin (early chapters in the manga, chp 15 I think) - so the ‘randomness’ of the power could be explained here as well.