.htaccess: Redirect 301 conflict with rewriterule - apache

Question

I recently updated an old website and I want to 301 all the old pages to the new version of each of them.
Here is my .htaccess
Options +FollowSymlinks -MultiViews
RewriteEngine On
#
# below are the 301 redirects
# **rules**
#
# below are the RewriteCond
# **rules**
#
# other stuff
#
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule .* - [L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^([^\.]+?)/?$ $1.php [NC,L]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteCond %{THE_REQUEST} ^(.+)\.php([#?][^\ ]*)?\ HTTP/
RewriteRule ^(.+)\.php$ /$1 [R=301,L]
The problem is that some of the old link are with the extension declared oldfile.html, others are just folders oldfolder/.
On the new version there are products, products/category and products/category/subcategory. These urls are generated with RewriteCond.
The following rule works:
Redirect 301 /category/ /products/category
The following does not work and instead redirects me to the home page.
Redirect 301 /old-folder/subcategory.html /products/category/subcategory
# /products/category/subcategory is also a RewriteRule
Here is the exact code in the .htaccess
# 301 rule
Redirect 301 /arredo-urbano/blocchi-standard.html /prodotti/arredo-urbano/001-blocchi-standard
# RewriteRule
RewriteRule ^prodotti/([^/]+)/([^/]+)/?$ prodotti.php?category=$1&subcategory=$2 [L]
I tried adding the [L] flag after each Redirect 301 so the rest of the .htaccess is ignored, but this causes a 500 Internal Error
All redirects are manually declared, with no regular expressions or wildcards and they are all spelled correctly.
Is there a way of making all redirect work as intended ? Also the thing that I do not understand is why the [L] flag causes an internal error.
Thank you

Answer 1

Three recommendations about redirect rules in general:
Keep redirect rules before internal rewrite rules
Keep specific patterns matching rules before generic pattern matching rules
Don't mix Redirect (mod_alias) rules with RewriteRule (mod_rewrite) rules.
Try these rules in your .htaccess:
Options +FollowSymlinks -MultiViews
RewriteEngine On
RewriteRule ^category/?$ /products/category [L,NC,R=301]
RewriteRule ^old-folder/subcategory\.html$ /products/category/subcategory [L,NC,R=301]
#
# below are the 301 redirects
# **rules**
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.php -f
RewriteCond %{THE_REQUEST} ^(.+)\.php([#?][^\ ]*)?\ HTTP/
RewriteRule ^(.+)\.php$ /$1 [R=301,L]
#
# below are the RewriteCond
# **rules**
#
# other stuff
#
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule .* - [L]
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule ^(.+?)/?$ $1.php [L]
Make sure to clear your browser cache before testing this change.