[MapProxy] get Error :Could not verify connection to URL (see logs for URL and reason)

[4 t]

Hello all,

I am working with Mapproxy 1.13.0 in combination with waitress as webserver
on windows to provide local working wmts services. Unfortunately, I
recently started getting the following error message on one of my systems:

"Could not verify connection to URL (see logs for URL and reason)."

as soon as a tile should be called. It makes no difference if I start
mapproxy in developer mode or provide the server service via waitress.

The exact same configuration works fine on another system and on a 3rd
system it seems to affect only one of my services.

When I connect and query local mbtiles they work. But the forwarding of the
WMTS services brings me the error message on one computer.

I have tried several Python versions.

Thanks in advance
David

config:

layer:
   - name: osm_german                           #online
     title: OpenStreetMap
     sources: [osm_german_cache]
caches:
    osm_german_cache:
        sources: [osm_german_tiles]
        format: image/png
        disable_storage: false
        grids: [GLOBAL_WEBMERCATOR]
sources:
    osm_german_tiles:
        type: tile
        url: https://a.tile.openstreetmap.de/%(tms_path)s.%(format)s
        grid: osm_grid
grids:
    osm_grid:
        srs: EPSG:900913
        origin: nw
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