@pichlo, @rinigus, WRT issues when searching a location and crashes / presumed OOM situations (as described by @pichlo):
As I had issues with the location search using OSM Scout Server (online services were always working fine) in the past (with Poor Maps / WhoGo Maps), I was eagerly reading this conversation and spontaneously tried to reproduce the experience.

While my use cases and usage is lighter than @pichlo's, my configuration is a bit "heavier":

• Jolla 1, SFOS 2.1.4, OSM Scout Server 1.9.1-1.76.1, recent Pure Maps
• Maps: OSM Scout Car Day English (vector)
• Navigation: Valhalla, 128 MByte cache (default)
• TTS engine: picotts
• Maps downloaded: NL, BE, LU, various DE states
• Search: Geocoder-NLP
• NLP languages: de, en, fr, lb, nl
• AlienDalvik is running, including two Android background tasks

1. I have not experienced crashes of Pure / WhoGo / Poor Maps or OSM Scout Server, as @Fellfrosch already indicated.
   When I drive the Jolla 1 phone ("sbj") into an OOM situation, e.g. by starting a fat Android app (Firefox works well) while using Pure / WhoGo / Poor Maps with OSM Scout Server, SailfishOS handles this as usual: UIs (OS & apps) become very unresponsive and SFOS regularly states "App XYZ is not responding. [Wait | Close]".
2. With above configuration and no other apps started, System Monitor shows ca. 630 MByte RAM and ca. 180 MB Swap used when browsing maps, searching for locations etc. in Pure Maps with OSM Scout Server (might be even less on a freshly rebooted device, it had an uptime of 4 days while testing).
   That is absolutely fine, Firefox alone consumes about the same amount of memory and one can still run a few smaller apps (regardless, if native or Android ones) concurrently.
3. In the past, location searches with libosmcout worked fine, albeit really slow (usually >> 1 minute), while I had trouble using Geocoder-NLP (not: "Valhalla") for location searches (except when submitting the full, comma separated, simple format: <House number>, <Street>, <City>), regularly running into "No results" (which rather looked like timeouts) after more than a minute of searching.
   @rinigus made me aware, that I still had "loading of libpostal on each call" switched on from past tests; switching it off made Geocoder-NLP's (not: "Valhalla's") location search consistently returning 25 really good matches within 30 to 40 seconds (as @rinigus expected). Aforementioned RAM usage does not significantly change, while doing this.

Hence from my experience, neither the OpenGL based rendering or Valhalla causes regular OOM situations on a SFOS device with 1 GB RAM and AlienDalvik running, although both (OGL & Valhalla) upped the RAM usage a bit further.

For me the only sore point on Jolla 1 phones is the stability of the TTS navigation (as discussed on Github and TMO).