While pol leadership has wilfully ignored this problem for its own benefits, the Army has been aware of it for long.
A report from Lt. Gen. SK Sinha, the then Governor of Assam, to the President in 1998 talks of it.
Read point 3 about Greater Bangaladesh

https://twitter.com/Kishkinda2/status/1284401597523480577?s=19

Even Muslim League ministry pushed Bangali Ms into Assam.
Viceroy Lord Wavell wrote, "The chief pol prob is the desire of the M Ministers to inc this immigration into the uncultivated Govt lands under the slogan of Grow More Food but what they are really after is Grow More Ms."

ML wanted Assam during partition. Jinnah declared that Assam was in his pocket. Cabinet Mission placed Assam in Group C with Bengal, it was accepted by ML & Congress high command but Lokapriya Gopinath Bordoloi opposed it. Grouping plan was failed & Assam was saved.

Not having Assam was & is a source of resentment.
Zulfikar Ali Bhutto wrote that Kashmir isn't the only point of contention b/w Indian & Pakistan, Assam is an equally imp dispute & Pak has good claims on it.
Then there's Mujibur's quote that I have already alluded to above.

These fckers have been after Assam since before independence, from when the Britishers first invited Bangali Musl!m labourers to work in the tea fields of Assam decades before independence.
They have systematically went after Assam all this while, & we slept.

Leading Bangladeshi intellectuals including diplomats have been making a case for "Lebensraum" - since Bangladeshi has too much population it is only natural for some of it to overflow into India's North East.
Like I said, they are more dangerous than Pakistan.

Political parties have encouraged illegal BD migration to get new votebanks, helped by corrupt officials & local Ms who hide them. But this much is already known.

Everyone should read this
SC Mullan, ICS & Census Superintendent of Assam, wrote in 1931, "the most imp even in last 25 years, worse than 1829 Burmese invasion, & one that destroy Assamese cultue & civilization wholescale is the invasion of Bengali Muslims into Assam"

He further compares them to an invading army & how they conquered Goalpara, comparing their movement with that of a large body of ants.
Demographic changes in the 3 undivided disrtricts of Goalpara, Kamrup & Nowgong from 1911 to 1931

SC Mullan back in 1931 used military terminology to describe the movement of Ms into Assam because he realised the strategic threat of it but our leaders never did.
Mullan also said apart from Sibsagar, in no district will Assamese feel at home. He was prophetic

In 1992, Hiteshwar Saikia the then Cong CM of Assam declared that there were no illegal migrants in Assam.
A young IAS tried to evict BD illegals from the island of Chawalkhao in 1982, he was promptly transferred, the same illegals were then given voting rights.
Congressi vermins

Between 1994 and 1997, enumeration of electors list in Assam by EC shows more than 30% increase in 17 assembly constituencies & over 20% increase in 40 constituencies.
Avg all India growth during this period was 7%, in Assam it was 16.4%. BD Ms made voters, Cong/AIUDF enjoy.