I'm afraid this issue still exists in SFML master in a non-determinisic way.
I get different availability of extensions and corresponding outputs of sf::err() for 32-bit and 64-bit Linux builds. This also affects RenderTexture (RenderTextureImplFBO works for me, RenderTextureImplDefault does not - seems to be related to GL contexts).
glxinfo lists all extensions as expected.
Ubuntu 16.04 Linux VM, HW accelerated (NV), hosted in Windows 7.
SFML master as of today.
32-bit build works, output of sf::err():
Setting vertical sync not supported
64-bit does not work, output of sf:err:
Warning: The created OpenGL context does not fully meet the settings that were requested
Requested: version = 1.1 ; depth bits = 0 ; stencil bits = 0 ; AA level = 0 ; core = false ; debug = false ; sRGB = false
Created: version = 0.0 ; depth bits = 24 ; stencil bits = 8 ; AA level = 0 ; core = false ; debug = false ; sRGB = false
Setting vertical sync not supported
sfml-graphics requires support for OpenGL 1.1 or greater
Ensure that hardware acceleration is enabled if available
OpenGL extension SGIS_texture_edge_clamp unavailable
Artifacts may occur along texture edges
Ensure that hardware acceleration is enabled if available