Merge CSS Files causes entire site to load Extremely Slow

[stevekem]

Steps to reproduce

1. Install Magento 2.0.4
2. Go to Admin > Stores > Configuration > Advanced > Developer
3. Enable "Merge CSS files"

Expected result

1. CSS files will be merged and site will load faster.

Actual result

1. Entire site runs EXTREMELY SLOW.
2. Both frontend and backend take 15-45 secs to load each page (cached). Product pages, checkout pages, admin pages are all affected.
3. Tried redeploying static files and flushing cache, does not help.
4. As soon as setting is disabled, site returns to normal.

[InCodeWeFly]

Renderer::renderAssetHtml($template, $assets)

// load much time
foreach ($assets as $asset)

$assets may not be array, so need to force the variable to array,

[Krapulat]

Same problem here.

[sbwcws]

Same issue here

[liquidia]

same issue works better without merging css / js

[wert2all]

Please, provide the used version. If the problem is actual for a specific branch, please, specify it and be sure that the latest update was used.

[Krapulat]

@wert2all At least with 2.0.7. When "Merge CSS" is activated, the system become very slow.