Refresh page with location fragment markers flash then disappear

[si-the-pie]

No markers appear when URL contains location fragment

No markers appeared on this visit to:
https://www.widenmypath.com/suggest/#12/51.4845/-0.1624 but they do appear once the map is dragged. (Try opening that link in a new incognito window.)

To reproduce:

1. Chrome > New Incognito Window

2. Open the Inspect window, select Network and filter for photomap

3. Paste https://www.widenmypath.com/suggest/#12/51.4845/-0.1624 into the incognito window and watch what happens

4. Page appears opened on London area. Sometimes the markers appear in a flash and then moments later they disappear, sometimes they don't appear at all.

5. Network log shows two calls to https://api.cyclestreets.net/v2/photomap.locations the first with a region covering the whole of the UK, the second covering the London area. These calls are issued at 1.22s and 1.33s. The first takes 600ms to respond, and the second 500ms.

6. The markers do appear when the map is dragged, and from then on it seems fine.

Also tried in Safari and Firefox with similar outcomes, although it does work sometimes.

I'm guessing at what might be the cause here, but maybe if a second call to the photomap API is performed before the first has responded then the result of the first call should be dropped.