As it parses, Python Scrapy is gradually decreasing in speed.

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This could be due to several factors such as:

1. Increased complexity of the website being scraped - if the website being scraped has a lot of pages or complex JavaScript, the parsing time may increase.

2. Poorly optimized code - if the code is not optimized, it can slow down the parsing process.

3. High traffic on the website - if there are a lot of people using the website at the same time, it can impact the speed of the parsing.

4. Poor internet connection - slow internet speed can slow down the parsing process.

To address these issues, some possible solutions include optimizing the code, using proxies, limiting the number of concurrent requests or increasing the timeout values.