@z428 It happens to me a lot, & tbh it's pretty exasperating. Because of it i frequently lose my reading place in my network timeline, & need to manually scroll up & down to "rediscover" where i was. This does not happen in my Masto* account.
I have a [non-technical, entirely guessed] hypothesis. I suspect that "interacting" with the subject post somehow "triggers" #Friendica to then check for new items in the fediverse, to insert at the top of my timeline, which then abruptly displaces my "reading point" down by the number & size of new posts added.
If true, i would mention this; Mastodon allows users to avoid this unpleasant inconvenience, by an optional #SlowMode setting in Preferences. When enabled [which many Masto users do, afaik], new toots are prevented from automatically entering the top of the timeline & displacing it down, instead generating a small notification atop the timeline noting the availability of new content. Then, at a time chosen by the user, they can manually click that actionable notice, which loads the new content. I really wish we had this in Friendica!