When browsing maps with OSM, everything works fine for a few seconds. After that it becomes virtually impossible as the download speed goes almost to zero, i.e. the download progress bar stops at, say, 10%, and hardly moves any further. This happens usually when zooming a location, and then stays like that, the maps becomes un-browsable.

It's not a simple connection problem - in the meantime the OSM WWW service works fine and fast. It seems to be related only to OSM, whereas other maps' data download fast, even those based on OSM, like the OpenTopoMap (OTM): if I switch to OTP, first the download speed is zero again, but when I restart Marble, OTM works fine. When restarted with OSM, the download is OK only for a very short time.

I tried increasing the RAM cache size (disk is unlimited), and deleting all the config files (from ~/.config and ~/.local) - to no avail.

When run through strace, there are several problems, I'm not sure if they are related to the OSM issue:

lstat("/usr", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/share", {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0
lstat("/usr/share/marble", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/share/marble/data", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/share/marble/data/maps", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/share/marble/data/maps/earth", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/share/marble/data/maps/earth/openstreetmap", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/usr/share/marble/data/maps/earth/openstreetmap/18", 0x7ffd68fa50d0) = -1 ENOENT (No such file or directory)
stat("", 0x7ffd68fa5210)                = -1 ENOENT (No such file or directory)
stat("/usr/share/marble/data", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
stat("/home/luke/.local/share/marble/maps/earth/openstreetmap/18/147143/89343.png", 0x7ffd68fa50c0) = -1 ENOENT (No such file or directory)

stat("/home/luke/.config/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/home/luke/.config/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/home/luke/.config/kde.org.conf", 0x7ffd68fa3780) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org/marble.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org/marble.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org/marble.conf", 0x7ffd68fa3780) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org.conf", 0x7ffd68fa3780) = -1 ENOENT (No such file or directory)
stat("/home/luke/.config/kde.org/marble.conf", {st_mode=S_IFREG|0664, st_size=176, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2705, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2705, ...}) = 0
stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2705, ...}) = 0
stat("/home/luke/.config/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/home/luke/.config/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/home/luke/.config/kde.org.conf", 0x7ffd68fa3780) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org/marble.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org/marble.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org/marble.conf", 0x7ffd68fa3780) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org.conf", 0x7ffd68fa37a0) = -1 ENOENT (No such file or directory)
stat("/etc/xdg/kde.org.conf", 0x7ffd68fa3780) = -1 ENOENT (No such file or directory)

Reproducible: Always

Steps to Reproduce:
1. Browse Maps with OSM
2. Zoom into some location
3. Browse maps a little bit

Actual Results:  
The download progress halts and hardly proceeds any further

Expected Results:  
Maps' data should be processed almost as fast as when using OSM online service

Marble Version 1.14.1 (stable release)
Fedora 24
KDE Frameworks 5.25.0
Qt 5.6.1 (built against 5.6.1)
The xcb windowing system